Systems and methods for conducting electrophysiological testing using high-voltage energy pulses to stun tissue

ABSTRACT

Systems and methods for diagnosing and treating tissue transmit an electrical energy pulse that temporarily stuns a zone of tissue, temporarily rendering it electrically unresponsive. The systems and methods sense an electrophysiological effect due to the transmitted pulse. The systems and methods alter an electrophysiological property of tissue in or near the zone based, at least in part, upon the sensed electrophysiological effect. The alteration of the electrophysiological property can be accomplished, for example, by tissue ablation or by the administration of medication. In a preferred implementation, radio frequency energy is used to both temporarily stun tissue and to ablate tissue through a common electrode.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation-in-part of U.S. applicationSer. No. 08/914,860, filed Aug. 19, 1997, which is a continuation ofU.S. which is a continuation of U.S. application Ser. No. 08/508,750,filed Jul. 28, 1995, now abandoned, each of which is incorporated hereinby reference.

BACKGROUND OF THE INVENTIONS

[0002] 1. Field of the Inventions

[0003] The inventions generally relate to systems and methods fordiagnosing or treating medical conditions.

[0004] 2. Description of the Related Art

[0005] There are many medical treatments which involve instances ofcutting, ablating, coagulating, destroying, or otherwise changing thephysiological properties of tissue (collectively referred to herein as“tissue modification”). For example, tissue modification can be used tochange the electrophysiological properties of tissue. Althoughtreatments that include tissue modification are beneficial, thephysiological changes to the tissue are often irreversible and themodification of tissue other than the intended tissue can disable oreven kill a patient. Accordingly, physicians must carefully select thetissue that is to be treated in this manner.

[0006] One area of medical treatment which involves tissue modificationis the ablation of cardiac tissue to cure various cardiac conditions.Normal sinus rhythm of the heart begins with the sinoatrial node (or “SAnode”) generating a depolarization wave front. The impulse causesadjacent myocardial tissue cells in the atria to depolarize, which inturn causes adjacent myocardial tissue cells to depolarize. Thedepolarization propagates across the atria, causing the atria tocontract and empty blood from the atria into the ventricles. The impulseis next delivered via the atrioventricular node (or “AV node”) and thebundle of HIS (or “HIS bundle”) to myocardial tissue cells of theventricles. The depolarization of these cells propagates across theventricles, causing the ventricles to contract. This conduction systemresults in the described, organized sequence of myocardial contractionleading to a normal heartbeat.

[0007] Sometimes aberrant conductive pathways develop in heart tissue,which disrupt the normal path of depolarization events. For example,anatomical obstacles in the atria or ventricles can disrupt the normalpropagation of electrical impulses. These anatomical obstacles (called“conduction blocks”) can cause the electrical impulse to degenerate intoseveral circular wavelets that circulate about the obstacles. Thesewavelets, called “reentry circuits,” disrupt the normal activation ofthe atria or ventricles. As a further example, localized regions ofischemic myocardial tissue may propagate depolarization events slowerthan normal myocardial tissue. The ischemic region, also called a “slowconduction zone,” creates errant, circular propagation patterns, called“circus motion.” The circus motion also disrupts the normaldepolarization patterns, thereby disrupting the normal contraction ofheart tissue.

[0008] The aberrant conductive pathways create abnormal, irregular, andsometimes life-threatening heart rhythms, called arrhythmias. Anarrhythmia can take place in the atria, for example, as in atrialtachycardia (AT), atrial fibrillation (AFIB) or atrial flutter (AF). Thearrhythmia can also take place in the ventricle, for example, as inventricular tachycardia (VT).

[0009] In treating VT and certain other arrhythmias, it is essentialthat the location of the sources of the aberrant pathways (calledsubstrates) be located. Once located, the tissue in the substrates canbe destroyed, or ablated, by heat, chemicals, or other means of creatinga lesion in the tissue. Ablation can remove the aberrant conductivepathway, restoring normal myocardial contraction. The lesions used totreat VT are typically relatively deep and have a large surface area.However, there are some instances where shallower lesions willsuccessfully eliminate VT.

[0010] The lesions used to treat AFIB, on the other hand, are typicallylong and thin and are carefully placed to interrupt the conductionroutes of the most common reentry circuits. More specifically, the longthin lesions are used to create a maze pattern which creates aconvoluted path for electrical propagation within the left and rightatria. The lesions direct the electrical impulse from the SA node alonga specified route through all regions of both atria, causing uniformcontraction required for normal atrial transport function.

[0011] The lesions finally direct the impulse to the AV node to activatethe ventricles, restoring normal atrioventricular synchrony.

[0012] Prior to modifying the electrophysiological properties of cardiactissue by ablation, or by other means of destroying tissue to createlesions, physicians must carefully determine exactly where the lesionsshould be placed. Otherwise, tissue will be unnecessarily destroyed. Inaddition, the heart is in close proximity to nerves and other nervoustissue and the destruction of this tissue will result in severe harm tothe patient.

[0013] With respect to the treatment of VT, physicians examine thepropagation of electrical impulses in heart tissue to locate aberrantconductive pathways. The techniques used to analyze these pathways,commonly called “mapping,” identify regions (or substrates) in the hearttissue which can be ablated to treat the arrhythmia. One form ofconventional cardiac tissue mapping techniques uses multiple electrodespositioned in contact with epicardial heart tissue to obtain multipleelectrograms. The physician stimulates myocardial tissue by introducingpacing signals and visually observes the morphologies of theelectrograms recorded during pacing, which this Specification will referto as “paced electrograms.” The physician visually compares the patternsof paced electrograms to those previously recorded during an arrhythmiaepisode to locate tissue regions appropriate for ablation. Theseconventional techniques require invasive open heart surgical techniquesto position the electrodes on the epicardial surface of the heart.

[0014] Conventional epicardial electrogram processing techniques usedfor detecting local electrical events in heart tissue are often unableto interpret electrograms with multiple morphologies. Such electrogramsare encountered, for example, when mapping a heart undergoingventricular tachycardia (VT). For this and other reasons, consistentlyhigh correct identification rates (CIR) cannot be achieved with currentmulti-electrode mapping technologies. In treating VT using conventionalopen-heart procedures, the physician may temporarily render a localizedregion of myocardial tissue electrically unresponsive during an inducedor spontaneous VT episode. This technique, called “stunning,” isaccomplished by cooling the tissue. If stunning the localize regioninterrupts an ongoing VT, or suppresses a subsequent attempt to induceVT, the physician ablates the localized tissue region. However, inconventional practice, cooling a significant volume of tissue to achievea consistent stunning effect is clinically difficult to achieve.

[0015] Another form of conventional cardiac tissue mapping technique,called pace mapping, uses a roving electrode in a heart chamber forpacing the heart at various endocardial locations. In searching for theVT substrates, the physician must visually compare all pacedelectrocardiograms (recorded by twelve lead body surfaceelectrocardiograms (ECG's)) to those previously recorded during aninduced VT. The physician must constantly relocate the roving electrodeto a new location to systematically map the endocardium.

[0016] These techniques are complicated and time consuming. They requirerepeated manipulation and movement of the pacing electrodes. At the sametime, they require the physician to visually assimilate and interpretthe electrocardiograms. Because the lesions created to treat VTtypically have a large volume, the creation of lesions that areimproperly located results in a large amount of tissue being destroyed,or otherwise modified, unnecessarily. Additionally, because thesetechniques do not distinguish between VTs that require a deep lesion,and VTs that can be treated with a more shallow lesion, tissue will beunnecessarily modified when a deep lesion is made to treat VTs that onlyrequire a more shallow lesion.

[0017] Turning to the treatment of AFIB, anatomical methods are used tolocate the areas to be ablated or otherwise modified. In other words,the physician locates key structures such as the mitral valve annulusand the pulmonary veins. Lesions are typically formed that blockpropagations near these structures. Additional lesions are then formedwhich connect these lesions and complete the so-called “maze pattern.”However, the exact lesion pattern, and number of lesions created, canvary from patient to patient. This can lead to tissue beingunnecessarily destroyed in patients who need fewer lesions than thetypical maze pattern.

[0018] Another issue that often arises in the treatment of AFIB isatrial flutters which remain after the physician finishes the mazeprocedure. Such flutters are the result of gaps in the lesions that formthe maze pattern. The gaps in the lesions must be located so thatadditional tissue modification procedures may be performed to fill inthe gaps. Present method of locating these gaps are, however, difficultand time consuming.

[0019] There thus remains a real need for systems and procedures thatsimplify the process of locating tissue that is intended for cutting,ablating, coagulating, destroying, or otherwise changing itsphysiological properties.

SUMMARY OF THE INVENTIONS

[0020] One aspect of a present invention provides systems and methodsfor conducting diagnostic testing of tissue. The systems and methodstransmit an electrical energy pulse that temporarily renders a zone oftissue electrically unresponsive. The systems and methods may also sensean electrophysiological effect due to the transmitted pulse. Based atleast in part upon the sensing of the electrophysiological effect, thephysician can determine whether the temporarily unresponsive tissue isin fact the tissue that is intended for modification. Thus, the presentinvention allows the physician to easily identify the tissue that isintended for modification, as well as tissue that is not.

[0021] In the area of cardiac treatment, for example, temporarilyrendering localized zones of myocardial tissue electrically unresponsiveallows the physician to locate potential pacemaker sites, slowconduction zones and other sources of aberrant pathways associated witharrhythmia. Using the same process, the physician can selectively alterconduction properties in the localized zone, without changingelectrophysiological properties of tissue outside the zone. With respectto the treatment of VT, the present invention allows a physician totemporarily create a large, deep area of electrically unresponsivetissue and then determine whether such tissue should be made permanentlyelectrically unresponsive by performing tests which show whether or notthe VT has been eliminated. When treating AFIB, the physician can createcontinuous long, thin areas of electrically unresponsive tissue and thenperform testing if required to insure that the permanent modification ofthe temporarily unresponsive tissue would create the desired therapeuticeffect. Similar techniques may also be used to precisely locate thesources of AF.

[0022] Once it is determined that the temporarily unresponsive tissue isthe tissue that should be permanently modified to cure the VT, AFIB orother arrhythmia, the physician can alter an electrophysiologicalproperty of the myocardial tissue in or near the diagnosed zone. Theelectrophysiological property of myocardial tissue can be altered, forexample, by ablating myocardial tissue in or near the zone. Thephysician will not ablate the tissue if the zone does not meetpreestablished criteria for ablation.

[0023] During procedures that are performed in and around neural tissue,physicians can render the tissue temporarily unresponsive prior topermanent modification. Tests can then be performed to determine whetherunwanted paralysis is present. If it is not, the physician can proceedwith modification.

[0024] In a preferred embodiment, the systems and methods use radiofrequency energy to both temporarily render tissue electricallyunresponsive as well as modify the tissue, should the establishedcriteria be met. The same electrode (or series of electrodes) may beused to transmit the radio frequency energy, which, in one mode,temporarily renders the tissue electrically unresponsive and which, in asecond mode, ablates or otherwise modifies the tissue.

[0025] Another one of the present inventions is an electrical energygenerating device. A preferred embodiment of the device includes a firstelement that, when activated, generates for transmission by an electrode(or series of electrodes) coupled to the device an electrical energypulse that temporarily renders tissue electrically unresponsive. Thedevice also comprises a second element that, when activated, generatesfor transmission by an electrode (or series of electrodes) coupled tothe device electrical energy to modify tissue by, for example, ablatingthe tissue. A switch may be provided which selects for activation eitherthe first element or the second element.

[0026] The above described and many other features and attendantadvantages of the present inventions will become apparent as theinvention becomes better understood by reference to the followingdetailed description when considered in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Detailed description of preferred embodiments of the inventionswill be made with reference to the accompanying drawings.

[0028]FIG. 1 is a diagrammatic view of a system for accessing a targetedtissue region in the body for diagnostic or therapeutic purposes inaccordance with one embodiment of a present invention.

[0029]FIG. 2 is an enlarged perspective view of a multiple-electrodestructure that may be used in association with the system shown in FIG.1.

[0030]FIG. 3 is an enlarged view of a tissue modification device thatmay be used in association with the system shown in FIG. 1.

[0031]FIG. 4 is a schematic view of a slow conduction zone in myocardialtissue and the circular propagation patterns (called circus motion) itcreates.

[0032]FIG. 5 is a diagrammatic view of a representative switchingelement in accordance with a preferred embodiment of a present inventionthat may be used in association with a radio frequency energy generatorto switch between a stunning mode and an ablation (or other tissuemodification) mode.

[0033]FIG. 6 is a perspective view of a flexible probe that includes aplurality of flexible electrodes in accordance with one embodiment of apresent invention.

[0034]FIG. 7 is a side view of a flexible probe that includes a flexibleelectrode and a tip electrode in accordance with one embodiment of apresent invention.

[0035]FIG. 8 is a side, partial section view of an exemplary flexibleelectrode in accordance with one embodiment of a present invention.

[0036]FIG. 9 is a side section view of the interior of the heart with aprobe in accordance with one embodiment of a present inventionpositioned transeptally against the septal wall of the left atrium.

[0037]FIG. 10 is an end view of the probe shown in FIG. 9.

[0038]FIG. 11 is a side section view of the interior of the heart withthe probe shown in FIG. 9 positioned against the septal wall of theright atrium.

[0039]FIG. 12A is a side view of a probe including a high density arrayof electrodes.

[0040]FIG. 12B is a side view of the probe shown in FIG. 12A with thearray of electrodes in a generally flat orientation.

[0041]FIG. 13A is a side view of an exemplary asymmetric electrodesupport device.

[0042]FIG. 13B is an end view of the exemplary asymmetric electrodesupport device shown in FIG. 13A.

[0043]FIG. 14 is a plan view of a system for stunning and/or modifyingtissue which includes an expandable porous electrode structure inaccordance with one embodiment of a present invention.

[0044]FIG. 15 is side view, with portions broken away, of a porouselectrode structure in accordance with one embodiment of a presentinvention in an expanded state.

[0045]FIG. 16 is side view of the porous electrode structure shown inFIG. 15 in a collapsed state.

[0046]FIG. 17 is an enlarged side view, with portions broken away, ofthe porous electrode structure shown in FIG. 15.

[0047]FIG. 18 is a side view, with portions broken away, of a porouselectrode structure in accordance with another embodiment of a presentinvention.

[0048]FIG. 19 is side, section view of the porous electrode structureshown in FIG. 18 in a collapsed state.

[0049]FIG. 20 is a section view taken generally along line 20-20 in FIG.17.

[0050]FIG. 21 is a side view of a porous electrode structure inaccordance with another embodiment of a present invention.

[0051]FIG. 22 is side view, with portions broken away, of a porouselectrode structure in accordance with still another embodiment of apresent invention.

[0052]FIG. 23 is a side view of a surgical device for positioning anoperative element within a patient in accordance with a preferredembodiment of a present invention.

[0053]FIG. 24 is a side, partial section view of a portion of thesurgical device shown in FIG. 23.

[0054]FIGS. 25 and 26 are front views of a spline assembly in accordancewith one embodiment of a present invention.

[0055]FIG. 27 is a partial front, partial section view of a surgicaldevice for positioning an operative element within a patient inaccordance with a preferred embodiment of a present invention.

[0056]FIG. 28 is a side view of a surgical device for positioning anoperative element within a patient in accordance with another preferredembodiment of a present invention.

[0057]FIG. 29 is a side, partial section view of an alternate tip thatmay be used in conjunction with the device shown in FIG. 28.

[0058]FIG. 30 is a section view of the distal portion of the deviceshown in FIG. 28 taken along line 30-30 in FIG. 28.

[0059]FIG. 31 a section view of an alternate distal portion for thedevice shown in FIG. 30.

[0060]FIG. 32 is a section view taken along line 32-32 in FIG. 28.

[0061]FIG. 33 is a section view showing an electrode coated withregenerated cellulose.

[0062]FIG. 34 is a section view showing a partially masked electrode.

[0063]FIG. 35 is a section view showing an alternative electrodeconfiguration.

[0064]FIG. 36 is a diagram showing one embodiment of a power supplycircuit in accordance with the present invention.

[0065]FIG. 37A is a diagram showing where an additional switching devicemay be added to the circuit shown in FIG. 36.

[0066]FIG. 37B is a detailed diagram of the switching device shown inFIG. 37A.

[0067]FIG. 38 is a schematic view of an exemplary graphical userinterface-based system including various diagnostic and therapeuticinstruments.

[0068]FIG. 39 is a schematic view of an exemplary graphical userinterface-based system including various diagnostic and therapeuticinstruments.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0069] The following is a detailed description of the best presentlyknown modes of carrying out the inventions. This description is not tobe taken in a limiting sense, but is made merely for the purpose ofillustrating the general principles of the invention.

[0070] The detailed description of the preferred embodiments isorganized as follows:

[0071] I. Mapping and Stunning-Modification Systems

[0072] A. Mapping Devices

[0073] B. Process Controller

[0074] C. Stunning-Modification Device

[0075] D. Power Supply

[0076] E. Electrode Selecting Device

[0077] F. Graphical User Interface-Based System

[0078] II. Additional Devices That May be Used in aStunning-Modification System

[0079] A. Multiple Electrode Stunning-Modification Devices

[0080] B. Structures For Positioning Electrodes in a Three-DimensionalArray

[0081] C. Expandable-CollapsiblePorous Electrode Structures

[0082] D. Surgical Probes

[0083] E. Regenerated Cellulose Coating

[0084] F. Temperature Sensors

[0085] III. Modes of Operation

[0086] A. Stunning Mode

[0087] B. Power Considerations Associated With Stunning

[0088] C. Modification Mode

[0089] D. Roving Pacing Mode

[0090] E. Electrophysiological Diagnosis Mode

[0091] IV. Bypass and Non-Bypass Environment Considerations

[0092] The section titles and overall organization of the presentdetailed description are for the purpose of convenience only and are notintended to limit the present invention.

[0093] I. Mapping and Stunning-Modification System

[0094]FIG. 1 shows an exemplary system 10 for analyzing endocardialelectrical events, using catheter-based, vascular access techniques inaccordance with one embodiment of a present invention. The system 10examines the depolarization of heart tissue that is subject to anarrhythmia and locates a potential tissue site for ablation or othermodification.

[0095] The exemplary system 10 shown in FIG. 1 includes a mapping probe14 and a multi-purpose stunning-modification probe 16. Each probe isseparately introduced into the selected heart region 12 through a veinor artery (typically the femoral vein or artery) through suitablepercutaneous access. The mapping probe 14 and multi-purposestunning-modification probe 16 can be assembled in an integratedstructure for simultaneous introduction and deployment in the heartregion 12. Further details of the deployment and structures of theprobes 14 and 16 are set forth in U.S. Pat. No. 5,636,634, entitled“Systems and Methods Using Guide Sheaths for Introducing, Deploying, andStabilizing Cardiac Mapping and Ablation Probes,” which is incorporatedherein by reference.

[0096] Other types of catheter-based mapping and stunning-modificationprobes may also be used. Additionally, the mapping and/orstunning-modification probes do not have to be catheter-based and can bein the form of probes that are inserted into the heart through athoracotomy, thoracostomy or median sternotomy. Examples of suchstructures are discussed in Section II-D below.

[0097] A. Mapping Devices

[0098] Exemplary mapping device 14 has a flexible catheter body 18. Thedistal end of the catheter body 18 carries a three-dimensionalmultiple-electrode structure 20. In the illustrated embodiment, thestructure 20 takes the form of a basket defining an open interior space22 (see FIG. 2). It should be appreciated that other three-dimensionalstructures could be used.

[0099] As FIG. 2 shows, the illustrated basket structure 20 comprises abase member 26 and an end cap 28. Generally flexible splines 30 extendin a circumferentially spaced relationship between the base member 26and the end cap 28.

[0100] The splines 30 are preferably made of a resilient, biologicallyinert material, like Nitinol metal or silicone rubber. The splines 30are connected between the base member 26 and the end cap 28 in aresilient, pretensed, radially expanded condition, to bend and conformto the endocardial tissue surface they contact. In the illustratedembodiment (see FIG. 2), eight splines 30 form the basket structure 20.Additional or fewer splines 30 could be used.

[0101] The splines 30 carry an array of electrodes 24. In theillustrated embodiment, each spline 30 carries eight electrodes 24. Ofcourse, additional or fewer electrodes 24 can be used.

[0102] A slidable sheath 19 is movable along the axis of the catheterbody 18 (shown by arrows in FIG. 2). Moving the sheath 19 forward causesit to move over the basket structure 20, collapsing it into a compact,low profile condition for introducing into the heart region 12. Movingthe sheath 19 rearward frees the basket structure 20, allowing it tospring open and assume the pretensed, radially expanded position shownin FIG. 2. The electrodes are urged into contact against the surroundingheart tissue.

[0103] Further details of a suitable basket structure are disclosed inU.S. patent application Ser. No. 08/206,414, filed Mar. 4, 1994, and PCTPublication No. WO 9421166, both entitled “Multiple Electrode SupportStructures.”

[0104] In use, the electrodes 24 sense electrical events in myocardialtissue for the creation of electrograms. The electrodes 24 areelectrically coupled to a process controller 32 (see FIG. 1). A signalwire (not shown) is electrically coupled to each electrode 24. The wiresextend through the body 18 of the device 14 into a handle 21 (see FIG.2), in which they are coupled to an external multiple pin connector 23.The connector 23 electrically couples the electrodes to the processcontroller 32.

[0105] Alternatively, multiple electrode structures can be locatedepicardially using a set of catheters individually introduced throughthe coronary vasculature (e.g., retrograde through the aorta or coronarysinus), as disclosed in PCT Publication No. WO 9416619, entitled“Multiple Intravascular Sensing Devices for Electrical Activity.”

[0106] B. Process Controller

[0107] In the illustrated embodiment, the process controller 32 induceselectrical events in heart tissue by transmitting pacing signals intoheart tissue. The process controller 32 senses these electrical eventsin heart tissue to process and analyze them to locate a potentialablation site.

[0108] More particularly (see FIG. 1), the process controller 32 iselectrically coupled by a bus 47 to a pacing module 48, which paces theheart sequentially through individual or pairs of electrodes to inducedepolarization. Details of the process controller 32 and pacing module48 are described in U.S. Pat. No. 5,494,042, entitled “Systems andMethods for Deriving Electrical Characteristics of Cardiac Tissue forOutput in Iso-Characteristic Displays.”

[0109] The process controller 32 is also electrically coupled by a bus49 to a signal processing module 50. The processing module 50 processescardiac signals into electrograms. A Model TMS 320C31 processoravailable from Spectrum Signal Processing, Inc. can be used for thispurpose.

[0110] The process controller 32 is further electrically coupled by abus 51 to a host processor 52, which processes the input from theelectrogram processing module 50. The output of the host processor 32can be selectively displayed for viewing by the physician on anassociated display device 54. The host processor 32 can be aPentium™-type or other suitable microprocessor. The exemplary processcontroller 32 operates in two functional modes, called the sampling modeand the matching mode.

[0111] Representative matching techniques to find potential ablationsites are described in U.S. patent application Ser. No. 08/390,559,filed Feb. 17, 1995, and PCT Publication No. WO 9625094, both entitled“Systems and Methods for Analyzing Biopotential Morphologies in BodyTissue.”

[0112] C. Stunning-Modification Device

[0113] The exemplary multi-purpose stunning-modification device 16 shownin FIG. 3 includes a flexible catheter body 34 that carries an electrode36 at the distal tip. The electrode is suitable for ablation and othertissue modification procedures. A handle 38 is attached to the proximalend of the catheter body 34. The handle 38 and catheter body 34 carry asteering mechanism 40 for selectively bending or flexing the catheterbody 34 along its length, as the arrows in FIG. 3 show. The steeringmechanism 40 can vary. For example, the steering mechanism can be asshown in U.S. Pat. No. 5,254,088, which is incorporated herein byreference.

[0114] A wire (not shown) electrically connected to the electrode 36extends through the catheter body 34 into the handle 38, where it iselectrically coupled to an external connector 45. The connector 45connects the electrode 36 to a generator 46, which supplieselectromagnetic radio frequency energy to the electrode 36. As used inthis Specification, the term “radio frequency energy” refers toelectrical energy with frequencies in the range of between about 10 kHzto about 3 GHz (3×10⁹ Hz). When operated in a uni-polar mode, anexternal patch electrode (not shown) constitutes the radio frequencyenergy return line. When operated in a bi-polar mode, an electrodecarried on the catheter body 34, or an electrode carried on a nearbycatheter, constitutes the radio frequency energy return line. Thegenerator 46 is operable through an associated switching element 80 intwo modes, called the stunning mode and the modification mode.

[0115] D. Power Supply

[0116]FIG. 36 illustrates one preferred embodiment of a power supplycircuit 500 for delivering controlled high voltage RF pulses to tissue.In the exemplary circuit, which is a full-wave bridge rectifier andtransformer circuit, a stepped up AC voltage from a variablycontrollable power source 502 is rectified into substantiallyunidirectional (rectified) pulse waveforms for application to bodytissue in a safe and controllable manner.

[0117] The circuit includes a first isolation and step-up transformer T1(preferably having a turns ratio of 10:1) through which power is inputfrom the AC power source 502, and four diodes D1, D2, D3 and D4, withoutput to the input terminal end of a RC circuit. The RC circuit has atleast one shunting capacitor C1, in parallel with resistors R1, R2 andR3 (resistors R1 and R2 are in series with one another and in parallelwith resistor R3). The output terminal end of the RC circuit is thevoltage drop across the capacitor C1. The RC circuit, which alsoincludes switching devices S1 and S2, can be thought of as resonant-typecircuit that stores energy supplied by the AC power supply through thefull-wave bridge rectifier, until such time that the RC circuit isselectively discharged through the primary coils of a second isolationand step-up transformer T2 by operation of switching device S1. Theswitching device S1 connects the transformer T2 with the output voltagedrop at capacitor C1. Output from transformer T2 is applied to a load,which is the body of the patient in the stunning and modificationsystems disclosed herein.

[0118] Inputting the AC power from AC power source 502 through the firstisolation and step-up transformer T1 provides at least two advantages.First, it allows the AC source voltage to be stepped up (or steppeddown) as needed. Second, it isolates the AC power source 502 from theremaining circuit, as shown with dashed lines in FIG. 36, therebyreducing the shock hazard to a patient. A similar function is providedby the second step-up and isolation transformer T2. Accordingly, theisolation and step-up transformers T1 and T2 electrically isolate theportion of the circuit circled with dotted lines from the patient andother circuits.

[0119] Step-up transformer T2 provides additional safety protection forthe patent, should switching device S1 fail in either the open or closedpositions. If switching device S1 fails in the open position, no poweris delivered, since no current flows through the primary coils oftransformer T2. If the switching device S1 fails in the closed position,substantially rectified voltage waveforms of long duration(predominately DC voltage waveforms) will flow through the primary coilsof transformer T2, and only minor variations in current will bereflected at the secondary coils. Thus, the patient is only exposed toRF pulsed voltage waveforms when S1 is properly working and rapidlybeing switched ON and OFF.

[0120] Operation of the exemplary full-wave bridge rectifier shown inFIG. 36 allows for substantial rectification of AC waveforms intosubstantially rectified or unidirectional pulsed waveforms (allowing forthe usual non-ideal behavior of actual circuits, ripple voltage, and thelike). The secondary voltage of transformer T1, seen at the output oftransformer T1, equals the turns ratio times the primary voltage, e.g.,V_(sec)=(N_(sec)/N_(pri))V_(pri). When the input cycle voltage waveformis positive, diodes D1 and D4 are forward-biased and conduct current inthe direction from node A to node B, and from node D to node C (node Dcan be connected to ground), with the portions of the circuit betweennodes A to D and nodes B to C being an open circuit by nature of diodesD2 and D3 being reverse biased. When the input cycle is negative, diodesD2 and D3 are forward-biased and conduct current in the direction fromnode C to node B and from node D to node A, with the portions of thecircuit between nodes D to C and nodes A to B being an open circuit, bynature of diodes D1 and D4 being reverse biased. A substantiallyfull-wave rectified output voltage appears across node 1 of the circuitand as seen by the RC circuit to the right of node 1.

[0121] Diodes D1-D4, which may be Zener diodes, must have reversebreakdown voltages that exceed the maximum voltage to which thecapacitor C1 can be charged. In one preferred embodiment, the diodesD1-D4 have a breakdown voltage of 300 V, and carry a maximum currentflow of less than or equal to 0.2 amperes RMS, while capacitor C1 has avalue of 10,000 μF, and is a high-voltage electrolytic capacitor, suchas the kind commonly used for flash cameras. Capacitor C1 can berepeatedly charged to 350-400 V, and may be connected in parallel withsimilar capacitors to achieve the necessary storage capacitance. Whencharged to 300 volts, capacitor C1 stores about 600 J of energy.

[0122] The input AC power is preferably about 5 W and 500 W. However, itshould be noted that relatively low levels of input power will reducethe overall flexibility of the system. For example, a 5 W input powersource would require at least 2 minutes to fully charge capacitor C1 tothe preferred level of about 600 J. Although a smaller capacitor orlower stored voltages would enable more rapid charging, the techniquesdisclosed herein require the storage of a significant amount of energyas well as rapid delivery to be effective. With respect to the upperpreferred limit, power levels higher than about 500 W increase thepotential for patient injury in the event of component failure.

[0123] The delivered power requirements for stunning targeted tissueusing the circuit shown in FIG. 36 is high. In some instances 800 V mustbe delivered into a 50 Ω load, requiring 12 kW of power. As noted inSection III-B with respect to the electrodes used in a three-dimensionalstructure, a RF pulse having an amplitude of 150 volts and a duration ofabout 10 ms will stun tissue to a depth of 5 mm, while a 800 volt RFpulse at 500 kHz frequency and a duration of 10 ms will stun a tissue toa depth of 10 mm. Delivery of this high level of power must be carefullycontrolled, since that level of power can severely injure a patient.

[0124] In some special circumstances, voltages as low as 100 V canelectrically stun tissue. On the other hand, a short burst of very highvoltages (about 4000 V) are often required to kill tissue by dielectricbreakdown of cell membranes. In order to account for these situations,the voltage outputs from transformer T1 should range from about 100 V toabout 4000 V.

[0125] In the preferred embodiment, the AC power supply 502 will deliverup to 50 W of power and have a maximum peak-to-peak voltage of 30 V,operating at a frequency of 10-100 kHz. The resistors R1 and R2 may havevalues of 10 Ω and 100 Ω, respectively, resulting in a decay timeconstant of about 2 minutes and an expected monitoring voltage of 0-3 Vacross R2. R3 is a power resistor with a resistance value of about 100Ω, which enables a more rapid adjustment of the voltage across capacitorC1, such as when the operator selects a lower stunning voltage. Thus,when switching device S2 is closed, the capacitor C1 is discharged, witha time constant of 1.4 sec.

[0126] Switching devices S1 and S2 may be switched ON and OFF to producea plurality of various amplitude and pulse width duration RF pulses.Switching devices S1 and S2 may be any suitable switching device,whether mechanical, electrical or electromechanical, and are preferablysolid state or power semiconductor switches such as an SCR, gateturn-off thyristor (GTO), power MOSFET, transistor, thyristor, or hybriddevices with FET input and a bipolar output stage. The switching devicesS1 are S2 are preferably controlled by a processor 504 (which may bepart of process controller 32 shown in FIG. 1 or a separate component),and/or with suitable computation circuits, where applicable, to producein conjunction with the circuit shown in FIG. 36 a plurality or train ofwaveform pulses of RF frequency at the output 2-2 of the circuit. Thesevoltage pulses are stepped up by transformer T2, having a turns ratio of4:1, for application to the patient.

[0127] Shunting resistors R1 and R2 can serve two purposes. First, whenthe AC power from power supply 502 is shut off, the resistors draincharge and reduce power from capacitor C1. Second, the voltage acrossresistor R2 is measured by the controller 504 and is used to control theAC power supply 502. The AC power supply can be controlled by thecontroller 504 to vary its output power and frequency.

[0128] To further provide for isolation, the voltage measurement ofresistor R2 by controller 504 may be made by optical isolation, or otherisolation measuring techniques such as magnetic isolation or telemetry.

[0129] The circuit of FIG. 36 controls the cycle length of the rectifiedRF pulse, the amplitude of the pulse, and the total duration of thepulse thorough selective discharge of the capacitor through theselective switching of the switching device S2, which discharges thecapacitor through shunting resistor R3, and selective switching ofswitching device S1, which creates a plurality of rectified RF pulsewaveforms that feed through step-up transformer T2. This produces a RFvoltage pulse train for application to the tissue in the patient's body.The duty cycle of the RF voltage pulse train may also be controlled bythe selective switching ON and OFF of switching device S1. The centerfrequency for the pulse waveform is preferably between about 100 kHz and1 MHz, with the waveform generated using ON/OFF duty cycles of from 10%to 50%. Frequencies above about 100 Mhz are not effective in a voltagestunning mode because dielectric absorption results in high heatingrates in the tissue, while frequencies below about 100 kHz can directlystimulate tissue, which is not desirable.

[0130] In one preferred embodiment, the switching device S1 is turned ONand OFF with a cycle length of 2 μsec and a duty cycle of 50%, for atotal pulse duration of 10 ms. To produce this pulse train, a train of5,000 1.0 μsec long pulses turn switching device S1 to the ON state, tocreate a 10 msec long 500 kHz pulse waveform at the output 2-2 of FIG.36, which are then suitably stepped up in voltage in a 4:1 ratio bytransformer T2 for output to the tissue.

[0131] The rectified AC waveform produced by turning switching device S1ON and OFF at a 500 kHz repetition rate would, in the absence offiltering, produce a nearly square wave. However, finite switching timesfor the switching device S1 and the transformer T2, which acts as abandpass filter, strongly filter out the higher harmonics of the basefrequency of the pulse waveform, resulting in a stunning waveform asapplied to tissue that can be made to be somewhat sinusoidal. Should amore perfect sinusoidal waveform be desired, using the teachings of thepresent invention one could produce a more perfect sinusoidal waveformby the tuning of the output transformer T2 to the center frequency ofthe pulse waveform used to stun tissue.

[0132] Energy outputted to the patient can be reduced by limiting thepower provided by the AC power supply 502 and the energy stored incapacitor C1. For one preferred embodiment of the invention, storedenergy at the capacitor C1 is 600 J and the AC power supply used tocharge C1 is limited to 50 W. Under maximum transfer rates, C1 isdischarged with a time constant of 77 msec. After several hundred msec,C1 is largely discharged, and the power delivery rate will drop to lessthan 30 W. Plateau power delivery rates to the patient are decreasedfrom 50 W at the AC power supply input to 30 W at the output due topower losses, such as losses in transformers T1 and T2.

[0133] It should be noted that the exemplary power supply circuit issusceptible to many variations. The only requirement is that power besupplied to a storage device and discharged from the storage device byway of a switching device that produces the desired pulses. For example,should it be found that their functionality is not required in aparticular application, the resistors in the RC circuit could beeliminated. Storage devices other than capacitors may be employed. TheAC power supply and rectifier arrangement illustrated in FIG. 36 may bereplaced by a battery (or plurality of batteries in series) and asuitable ON/OFF switch. Also, the transformer T2 can be replaced byanother type of inductive device.

[0134] E. Electrode Selecting Device

[0135] As discussed in Section III-A, a sequence of stunning pulses canbe applied with different electrodes in a multiple electrode structure(such as those discussed in Section II and shown in FIGS. 10-13B) tocreate a complex pattern of temporarily unresponsive tissue. One exampleof an electrode selecting device that may be used to switch from one (ormore) electrodes to another (or more) electrodes in, for example thecircuit shown in FIG. 36, is shown in FIGS. 37A and 37B. Exemplaryswitching device S3 includes a plurality of mechanical orelectromechanical switches SW₁-SW_(N). Preferably, each switchSW₁-SW_(N) is associated with an individual electrode E₁-E_(N). Thus,the state of the switch SW determines whether the associated electrodewill deliver the stunning voltage.

[0136] Relay or mechanical switches are preferred because these switchescan have very low coupling capacitances across the switch, as comparedto single solid state power switches. The switches should normally beopen in order to promote patient safety and minimize the switching powerrequirements.

[0137] Should relatively fast switching times be desired, four or moreswitches with relatively low ON resistances could be used in series,thereby decreasing the effective capacitance across the switch. Here,the switch SW may be formed from multiple solid state switches inseries. It should be noted, however, that such an arrangement willgreatly complicate the switch drive circuitry.

[0138] F. Graphical User Interface-Based System

[0139] One example of a graphical user interface-based system that maybe used to sequentially apply either a single high voltage pulse or aseries of high voltage pulses to tissue is illustrated in FIGS. 38 and39. In the illustrated embodiment, the system 310 includes an instrument312 (such as a catheter or surgical probe) having an array of electrodes318, as well as instruments 314 and 316, which include operativeelements usable for diagnostic or therapeutic purposes. One exemplaryoperative element is a device for imaging body tissue, such as anultrasound transducer or an array of ultrasound transducers, an opticfiber element, or a CT or MRI scanner. Other exemplary operativeelements include device to deliver drugs or therapeutic material to bodytissue, or electrodes for sensing a physiological characteristic intissue or transmitting energy to stimulate or ablate tissue.

[0140] The exemplary system 310 includes one or more instrumentcontrollers (designated 320, 322, and 324) which, in use, condition theassociated instrument 312, 314, and 316 to perform its respectivediagnostic or therapeutic function. To aid in coordinating signal anddata flow among the controllers 320, 322, and 324 and their linkedinstruments, the system 310 includes an interface 326 (or “masterswitching unit) that establishes electrical flow paths and processes thevarious diagnostic or therapeutic data and signals in an organized andefficient fashion. A suitable interface is disclosed in U.S. applicationSer. No. 08/770,971, entitled “Unified Switching System forElectrophysiological Stimulation and Signal Recording and Analysis,”filed Dec. 12, 1996, and incorporated herein by reference.

[0141] The exemplary system 310 also includes a main processing unit(MPU) 328, which is preferably a Pentium™ microprocessor. The MPU 328includes an input/output (I/O) device 330, which controls and monitorssignal and data flow to and from the MPU 328. The I/O device 330 can,for example, consist of one or more parallel port links and one or moreconventional serial RS-232C port links or Ethernetm communication links.The I/O device 330 is coupled to a data storage module or hard drive332, as well as to the instrument interface 326 and a printer 334. Anoperator interface module 336, which is coupled to the I/O device 330,includes a graphics display monitor 338, a keyboard input 340, and apointing input device 342, such as a mouse or trackball. The graphicsdisplay monitor 338 can also provide for touch screen (finger or stylus)input. An operating system 344 for the MPU 328 may, for example, resideas process software on the hard drive 332, which is down loaded to theMPU 328 during system initialization and startup. In the illustratedembodiment, the operating system 344 executes through the operatorinterface 336 a graphical user interface (GUI) 346.

[0142] The operating system 344 administers the activation of a library348 of control applications, which are designated, for purpose ofillustration, as A1 to A7 in FIG. 38. In the illustrated embodiment, thecontrol applications A1 to A7 all reside in storage 354 as processsoftware on the hard drive 332 and are down loaded and run based uponoperator input through the GUI 346. Each control application A1 to A7prescribes procedures for carrying out given functional tasks. Ofcourse, the number and functions of the applications A1 to A7 can vary.Exemplary functions include clinical procedures, specialized navigationapplications, and utility applications.

[0143] Clinical procedure applications contain the steps to carry out aprescribed clinical procedure, such as the sequential application ofstunning pulses to predetermined electrodes in a two orthree-dimensional array. A number of such applications may be stored,each corresponding to an area, or areas, of stunned tissue havingvarious shapes and sizes. That way, the physician need only select thedesired shape with the GUI 346 to form the desired area of temporarilyunresponsive tissue. Similar application programs may be used to formareas of permanently unresponsive tissue using the high voltagepulse-based modification techniques described in Section III-C below.

[0144] The navigation applications allow the operator to visualize onthe GUI 346 the orientation of the multiple electrode array 312 andinstruments 314 and 316, thereby assisting the operator in manipulatingand positioning the array and instruments. For example, one navigationapplication may construct an ideal or virtual image of the deployedarray and the instruments, while the other displays an actual, real-timeimage of each.

[0145] Utility applications carry out system testing, system servicing,printing, and other system support functions affecting the applications.

[0146] When run by the operating system 344, each application generatesprescribed command signals, which the I/O device 330 distributes via theinstrument interface 326 to condition the instrument controllers 320,322, and 324 to perform a desired task using the instruments 312, 314,and 316. The I/O device 326 also receives data from the instrumentcontrollers 320, 322, and 324 via the instrument interface 326 forprocessing by the procedure application being run. The GUI 346 presentsto the operator, in a graphical format, various outputs generated by theprocedure application run by the operating system 344 and allows theuser to alter or modify specified processing parameters in real time.

[0147] The operating system 344 also includes one or more specialtyfunctions (designated F1 and F2 in FIG. 38), which run in the backgroundduring execution of the various applications A1 to A7. For example, onefunction F1 can serve to establish and maintain an event log 350 whichkeeps time track of specified important system events as they occurduring the course of a procedure. Another function F2 can serve toenable the operator, using the GUI 346, to down load patient specificinformation generated by the various applications A1 to A7 to the harddrive 332 as data base items, for storage, processing, and retrieval,thereby making possible the establishment and maintenance of a patientdata base 352 for the system 310.

[0148] As illustrated in FIG. 39, the exemplary multiple electrode arrayis a three-dimensional basket structure 358 carried at the distal end356 of a catheter or surgical probe. The exemplary basket structureincludes eight spaced apart spline elements (alphabetically designated Ato H in FIG. 39) assembled together by a distal hub 360 and a proximalbase 362. Each spline carries eight electrodes which are numericallydesignated on each spline from the most proximal to the most distalelectrode as 1 to 8. The basket structure 358 thus supports a total ofsixty-four electrodes. Of course, a greater or lesser number of splineelements and/or electrodes can be present. Each of the electrodes iselectrically connected to an individual conductor in a multipleconductor cable 364. The splines can either be arranged symmetrically,as shown in FIG. 39, or asymmetrically as shown in FIGS. 13A and 13B toprovide a high density electrode array. A stunning energy source 380 canalso be coupled to the electrodes, either through the instrumentinterface 326 (as shown in solid lines in FIG. 39), or through its owninstrument interface 326″ (shown in phantom lines in FIG. 39) coupled tothe MPU 328.

[0149] Instrument 314 may be carried at the distal end 366 of a catheteror surgical probe. In the illustrated embodiment, instrument 314includes an electrode 368 for sensing electrical activity in tissue, aswell as to transmitting energy to stimulate or ablate tissue. Theelectrode 368 is electrically connected by a cable 370 to the instrumentinterface 326. A generator 378 for transmitting radio frequency ablationenergy can also be coupled to the electrode 368, either through theinstrument interface 326 (as shown in solid lines in FIG. 39), orthrough its own instrument interface 326′ (shown in phantom lines inFIG. 39) coupled to the MPU 328. Instrument 316, which may be carried atthe distal end of a catheter or surgical probe, includes an imagingdevice 372 which operates using a visualizing technique such asfluoroscopy, ultrasound, CT, or MRI, to create a real-time image of abody region. A cable 376 conveys signals from the imaging device 372 tothe instrument interface 326.

[0150] Clinical procedure applications can also be designed andimplemented during a procedure using the GUI 346. Based on the imagesprovided by the navigation applications of the electrode supportstructure, the physician can select the electrodes that will produce thedesired area, or areas, of permanently or temporarily unresponsivetissue. The image of the electrode support structure will preferablyappear as it does in FIG. 39, i.e. with the spline letters andelectrodes numbers visible. The desired electrodes can be selected usingthe keypad by typing the spline element letters and electrode number.For example, A5, B5 and C5 can be selected to produce an area whichspans spline elements, or A3, A4 and A5 can be selected to produce anarea which extends along a single spline element. Alternatively, theelectrodes may be selected by way of the touch screen or pointingdevice.

[0151] Unless otherwise desired, the pulses will occur in the order thatthe electrodes are selected. Other information, such as pulse length,time between pulses, pulse magnitude, etc. can also be input via the GUI346. Instead of delivering energy sequentially, the system can beconfigured such that a plurality of electrodes transmit energysimultaneously. Such simultaneous transmission may be part of a sequencethat includes other electrodes transmitting energy simultaneously orindividually. This feature may also be selected on the GUI 346.

[0152] Additional information concerning the GUI-based systemillustrated in FIGS. 38 and 39 may be found in U.S. application Ser. No.09/048,629, entitled “Interactive Systems and Methods For Controllingthe Use of Diagnostic or Therapeutic Instruments in Interior BodyRegions,” filed Mar. 26, 1998, and incorporated herein by reference.

[0153] II. Additional Devices That May be Used in aStunning-Modification System

[0154] A. Multiple Electrode Stunning-Modification Probes

[0155] Probe configurations employing multiple electrodes may also beused to form continuous, elongate areas of modified or temporarilyelectrically unresponsive (i.e. “stunned”) tissue. Such areas may beeither straight or curvilinear. Examples of such multiple electrodeprobes are shown in U.S. Pat. Nos. 5,545,193 and 5,582,609, both ofwhich are incorporated herein by reference.

[0156] As shown by way of example in FIG. 6, an exemplary multipleelement probe 100 includes a plurality of segmented, generally flexibleelectrodes 102 carried on a flexible body 104. The flexible body 104 ismade of a polymeric, electrically nonconductive material, likepolyethylene or polyurethane, and preferably carries within it aresilient bendable wire or spring with attached steering wires so it canbe flexed to assume various curvilinear shapes. The electrodes 102 arepreferably spaced apart lengths of closely wound, spiral coils made ofelectrically conducting material, like copper alloy, platinum, orstainless steel. The electrically conducting material can be coated withplatinum-iridium or gold to improve its conduction properties,radiopacity and biocompatibility. Instead of a single length of woundwire, one or more of the electrodes 102 may be formed from multiple,counter wound layers of wire. The electrodes may also be formed from ahypotube that is machined into a coil. Additionally, the other electrodestructures disclosed in the present specification may also be used incombination with this embodiment.

[0157] Alternatively, a ribbon of electrically conductive material canbe wrapped about the flexible body 104 to form a flexible electrode.Flexible electrodes may also be applied on the flexible body by coatingthe body with a conductive material, like platinum-iridium or gold,using conventional coating techniques or an ion beam assisted deposition(IBAD) process. For better adherence, an undercoating of nickel ortitanium can be applied.

[0158] In another preferred embodiment, and as shown by way of examplein FIG. 7, a generally rigid tip electrode 106 may be combined with thegenerally flexible electrodes. Of course, the tip electrode 106 could bea generally flexible electrode structure made of a closely wound coil orother flexible material. Temperature sensing elements 298, such asthermocouples or thermistors, may also be provided. Temperature sensingis discussed in detail in Section II-F below.

[0159] The flexible body 104 can be remotely steered to flex it into adesired shape, or it can possess a preformed shape. In the lattersituation, removing a constraint (such as a sheath, not shown), enablesthe operator to change the segment from straight to curvilinear. Theprobe body may also be formed from a malleable material, which isespecially useful when the probe is part of a surgical probe that is notcatheter-based. Such probes are discussed in Section II-D below.

[0160] The number of electrodes and the spacing between them, can vary,according to the particular objectives of the therapeutic procedure. Forexample, the probe shown in FIG. 6 is well suited for creatingcontinuous, elongated lesion patterns (or patterns of tissue modified inother ways) as well as continuous, elongated areas of stunned tissue,provided that the electrodes are adjacently spaced close enough togetherto create additive heating/stunning effects when energy is transmittedsimultaneously to the adjacent electrodes. The additive heating effectsbetween close, adjacent electrodes intensifies the desired effect on thetissue contacted by the electrodes. The additive heating effects occurwhen the electrodes are operated simultaneously in a bipolar modebetween electrodes or when the electrodes are operated simultaneously ina unipolar mode, transmitting energy to an indifferent electrode.

[0161] More particularly, when the spacing between the electrodes isequal to or less than about 3 times the smaller of the diameters of theelectrodes, the simultaneous emission of energy by the electrodescreates an elongated continuous lesion pattern, or area of stunnedtissue, in the contacted tissue area due to the additive effects.Similar effects are obtained when the spacing between the electrodes isequal to or less than about 2 times the longest of the lengths of theelectrodes.

[0162] To consistently form long, thin, continuous curvilinear lesionpatterns or areas of electrically unresponsive tissue, additionalspatial relationships among the electrodes must be observed. When thelength of each electrode is equal to or less than about 5 times thediameter of the respective electrode, the curvilinear path that theprobe takes should create a distance across the contacted tissue areathat is greater than about 8 times the smaller of the diameters of theelectrodes. The simultaneous application of energy will form acontinuous elongate lesion pattern, or area of stunned tissue, thatfollows the curved periphery contacted by the probe, but does not spanacross the contacted tissue area. The same effect will be obtained whenthe length of each electrode is greater than about 5 times the diameterof the respective electrode, and the curvilinear path that supportelement takes should create a radius of curvature that is greater thanabout 4 times the smallest the electrode diameters. Of course, thespacing between the electrodes must be such that additive heatingeffects are created.

[0163] Taking the above considerations into account, it has been foundthat adjacent electrode segments having lengths of less than about 2 mmdo not consistently form the desired continuous lesions. Suchconstraints do not apply to areas of stunned tissue. Techniques to stuntissue to 5 mm to 10 mm in depth using small electrodes are discussed inSection III-B. For ablation purposes, flexible electrode elements canrange from 2 mm to 50 mm in length and are preferably 12.5 mm in lengthwith 2 to 3 mm spacing. The diameter of the electrodes and underlyingflexible body can vary from about 4 French to about 10 French incatheter-type probes. The tip electrode is preferably from 4 mm to 10 mmin length.

[0164] The flexibility of the coil electrodes can be increased byspacing the individual coil windings, which increases the ability of thewindings to closely conform to irregular anatomical surfaces. Thewindings of electrodes should be spread apart by a distance that is atleast ⅕ of the width of the material that makes up the individual coils.Preferably, the distance is ½ of the width. Referring to FIG. 8, thedistance D can also vary along the length of the electrode. Here, theelectrode 110 includes a first zone 112 of windings that are spacedapart and two second zones 114 of windings that are closely adjacent toone another. The closely spaced zones provide a support structure fortemperature sensing elements, which as discussed below in Section II-F,may be advantageously placed at the longitudinal ends of the electrode.Although the exemplary electrode shown in FIG. 8 has a rectangularcross-section, other configurations, such as a round cross-section, canalso be employed.

[0165] Power can be supplied to the electrodes individually or, asdescribed above, the power can be simultaneously supplied to more thanone or even all of the electrodes. The supply of power to the electrodescan be controlled in the manner disclosed in U.S. Pat. No. 5,545,193.

[0166] B. Structures For Positioning Electrodes in a Three-DimensionalArray

[0167] There are many instances where it is advantageous to positionelectrodes in a three-dimensional array. For example, the interatrialseptum (identified by the letter S in FIG. 9) has been shown to be ajunction for the propagation of atrial fibrillation wavelets. FIGS. 9and 10 show a device 116 adapted to locate multiple electrodes 118against a large area of the interatrial septum (S). The device 116 maybe used in the same manner as the mapping device 14 shown in FIG. 2. Thedevice may also be used to deliver RF energy to ablate tissue. Forexample, a subset of the electrodes on the array can be used tosimultaneously deliver RF energy to the tissue contacting theelectrodes. The subset is chosen based on the geometry and dimensions ofthe region to be ablated. The region may be a long, continuous line usedto treat AFIB, a large circular area used to treat the subendocardialsubstrates that cause VT, or any other geometry necessary to ablate thesubstrate(s) causing a particular physiologic event.

[0168] Although device 116 is shown as part of a catheter-based device,it may also be employed in a surgical probe that is not catheter-based.Such probes are discussed in Section II-D below.

[0169] The device 116 includes an array of spline elements 120 thatradiate in a star-like pattern from the distal end 122 of a cathetertube 124 (as the end view in FIG. 10 best shows). Each spline element120 carries multiple electrodes 118. As shown by way of example in FIG.9, the catheter tube 124 is deployed through a conventional transeptalsheath 126 into the left atrium. During introduction, the sheath 126encloses the device 116, maintaining the device in a collapsedcondition. Once located in the left atrium, the sheath 126 is pulledback past the septum S, and the spline elements 120, freed of the sheath126, spring open. The physician pulls the catheter tube 124 back tobring the electrodes 118 into contact against the septal wall within theleft atrium.

[0170] Turning to FIG. 11, the device 116 can be deployed in the rightatrium by introduction through the sheath 126. Retraction of the sheath126 allows the spline elements 120 to spring open. The physician pushesthe catheter tube 124 toward the septum S to place the electrodes 118into contact against the septal wall within the right atrium.

[0171] Another device, generally represented by reference numeral 128 inFIGS. 12A and 12B, includes a high density array of electrodes 130 thatcan be placed against the septal wall in the right atrium, or againstanother region anywhere within the heart. The device 128 includes anarray of spline elements 132 constrained between a proximal anchor 134and a distal hub 136. The device 128 is attached to the distal end 138of a catheter tube 140. However, it may also be employed in a surgicalprobe that is not catheter-based.

[0172] The spline elements 132 carry the electrodes 130 such that theyare concentrated in a high density pattern about the distal hub 136.Away from the distal hub 136, the spline elements 132 are free ofelectrodes 130.

[0173] A stylet 142 extends through the catheter tube bore 144 and isattached at its distal end to the distal hub 136. The proximal end ofthe stylet 142 is attached to a push-pull control mechanism 146 in thecatheter tube handle 148. As FIG. 12B shows, pulling back on themechanism 146 (arrow 147) draws the distal hub 136 toward the proximalanchor 134. The distal region of the spline elements 132 bend and deformoutward, to form a generally planar surface 150 radiating about thedistal hub 136, on which the electrodes 130 are located. The surface 150presents the high density pattern of electrodes 130 for intimate surfacecontact with a large region of heart tissue. The distal hub 136 can bemade of an energy transmitting material and serve as an electrode toincrease the electrode density.

[0174]FIGS. 13A and 13B show another example of a device (or “supportassembly”) that may be used to position a high density array ofelectrodes against a bodily structure. The support assembly 129 can beattached to the distal end of a catheter or surgical probe and includesan array of flexible spline elements 131 extending longitudinallybetween a distal hub 133 and a base 135. The geometry of the assembly129 is asymmetric in a radial sense. That is, when viewed from distalhub 133, as FIG. 13B shows, the spline elements 131 do not radiate fromthe main axis at generally equal circumferential intervals. Instead,there are at least some adjacent spline elements 131 that arecircumferentially spaced apart more than other adjacent spline elements131. The largest angle measured between two adjacent spline elements inthe assembly (designated angle α in FIG. 13B) preferably exceeds thesmallest angle measured between two other adjacent spline elements(designated angle β in FIG. 1 3B).

[0175] Due to the radial asymmetry of the assembly 129, not all thespline elements 131 need to carry electrodes 137. The geometry of theassembly 129 is symmetric in an axial sense. The proximal region 139 andthe distal region 141 of each spline are, or capable of being, occupiedby electrodes 137.

[0176] The exemplary embodiment shown in FIGS. 13A and 13B includes tenspline elements 131, designated S1 to S10. The exemplary asymmetricarrangement includes a first discrete group 145 of five adjacent splineelements 131 (S1 to S5) and a second discrete group 149 (S6 to S10). Thegroups 145 and 149 are shown to be diametrically arranged, and eachgroup 145 and 149 occupies an arc of about 90°. Within each group, theadjacent spline elements S1 to S5 and S6 to S10 are circumferentiallyspaced apart in equal intervals of about 22° (which comprises angle β).However, the spline elements S1/S10 and S5/S6, marking the boundariesbetween the groups 145 and 149, are circumferentially spaced fartherapart, at about 90° (which comprises angle α). This non-uniformcircumferential spacing of the spline elements 131 exemplifies one typeof radially asymmetric structure.

[0177] Preferably, the distance between electrode s on different splineelements within a group of spline elements (such as S1 to S5) is equalto the distance between electrodes on a spline element within the group.In other words, the distance between two adjacent electrodes on a splineelement is the same as the distance between two adjacent electrodesrespectively located on adjacent spline elements. Such an arrangementsimplifies the process of forming complex two-dimensional patterns (orlarge areas) of stunned or permanently modified tissue.

[0178] Other types of asymmetric structures for positioning electrodesin a three-dimensional array, such as axially asymmetric structures, aredisclosed in U.S. patent application Ser. No. 08/742,569, entitled“Asymmetric Multiple Electrode Support Structures,” filed Oct. 28, 1996,which is incorporated herein by reference.

[0179] C. Expandable-Collapsible Porous Electrode Structures

[0180] Device configurations employing expandable-collapsible porouselectrode structures can be used to form areas of modified ortemporarily unresponsive tissue that are either large and deep, smalland shallow, or large and shallow. Examples of such devices are shown inFIGS. 15-22. These devices may be used in the same manner as the deviceshown in FIGS. 1 and 3. Additionally, although the devices shown inFIGS. 15-22 are part of catheter-based devices (such as that shown inFIG. 14), the features of the devices may be employed in surgical probesthat are not catheter-based. Such probes are discussed in Section II-Dbelow.

[0181] Additional information concerning expandable-collapsible porouselectrode structures, which are preferably formed from regeneratedcellulose, can be found in U.S. patent application Ser. No. 08/631,575,entitled “Tissue Heating and Ablation Systems and Methods Using PorousElectrode Structures,” which is incorporated herein by reference.

[0182] 1. Expandable-Collapsible Porous Electrode StructureConfigurations

[0183]FIG. 14 shows a tissue modification-stunning system 152 thatincludes a flexible catheter tube 154 with a proximal end 156 and adistal end 158. The proximal end 156 carries a handle 160. The distalend 158 carries an electrode structure 162. As shown by way of examplein FIGS. 15 and 20, the electrode structure 162 includes anexpandable-collapsible body 164. The geometry of the body 164 can bealtered between a collapsed geometry (FIG. 16) and an enlarged, orexpanded, geometry (FIG. 15). In the illustrated embodiments, liquidpressure is used to inflate and maintain the expandable-collapsible body164 in the expanded geometry.

[0184] As illustrated for example in FIGS. 14-16, the catheter tube 154carries an interior lumen 166 along its length. The distal end of thelumen 166 opens into the hollow interior of the expandable-collapsiblebody 164. The proximal end of the lumen 166 communicates with a port 168on the handle 160. The liquid inflation medium 170 is conveyed underpositive pressure through the port 168 and into the lumen 166. Theliquid medium 170 fills the interior of the expandable-collapsible body164. The liquid medium 170 exerts interior pressure to urge theexpandable-collapsible body 164 from its collapsed geometry to theenlarged geometry.

[0185] This characteristic allows the expandable-collapsible body 164 toassume a collapsed, low profile (ideally, less than 8 French diameter,i.e., less than about 0.267 cm) when introduced into the vasculature.Once located in the desired position, the expandable-collapsible body164 can be urged into a significantly expanded geometry of, for example,approximately 5 mm to 20 mm. Expandable-collapsible bodies with largerprofiles may be used in conjunction with probes that are notcatheter-based.

[0186] As shown by way of example in FIGS. 18 and 19, the structure 162can include, if desired, a normally open, yet collapsible, interiorsupport structure 172 to apply internal force to augment or replace theforce of liquid medium pressure to maintain the body 164 in the expandedgeometry. The form of the interior support structure 172 can vary. Itcan, for example, comprise an assemblage of flexible spline elements174, as shown in FIG. 18, or an interior porous, interwoven mesh or anopen porous foam structure.

[0187] The exemplary internally supported expandable-collapsible body164 is brought to a collapsed geometry, after the removal of theinflation medium, by outside compression applied by an outer sheath 178(see FIG. 19), which slides along the catheter tube 154. Forwardmovement of the sheath 178 advances it over the expandedexpandable-collapsible body 164. The expandable-collapsible body 164collapses into its low profile geometry within the sheath 178. Rearwardmovement of the sheath 178 retracts it away from theexpandable-collapsible body 164. Free from the confines of the sheath178, the interior support structure 172 springs open to return theexpandable-collapsible body 164 to its expanded geometry to receive theliquid medium.

[0188] As illustrated for example in FIG. 18, the structure 162 furtherincludes an interior electrode 180 formed of an electrically conductivematerial carried within the interior of the body 164. The material ofthe interior electrode 180 has both a relatively high electricalconductivity and a relatively high thermal conductivity. Materialspossessing these characteristics include gold, platinum,platinum/iridium, among others. Noble metals are preferred. An insulatedsignal wire 182 is coupled to the electrode 180. The signal wire 182extends from the electrode 180, through the catheter tube 154, to anexternal connector 185 on the handle 160. The connector 185 electricallycouples the electrode 180 to a radio frequency generator.

[0189] In accordance with the exemplary embodiments, the liquid medium170 used to fill the body 164 includes an electrically conductiveliquid. The liquid 170 establishes an electrically conductive path,which conveys radio frequency energy from the electrode 180. Inconjunction, the body 164 comprises an electrically non-conductivethermoplastic or elastomeric material that contains pores 184 on atleast a portion of its surface. The pores 184 of the body 164 (showndiagrammatically in enlarged form for the purpose of illustration)establishes ionic transport of the tissue stunning or modificationenergy from the electrode 180, through the electrically conductivemedium 170, to tissue outside the body. Preferably, the liquid 170possesses a low resistivity to decrease ohmic loses, and thus ohmicheating effects, within the body 164. In the illustrated and preferredembodiment, the liquid 170 also serves the additional function as theinflation medium for the body, at least in part.

[0190] The composition of the electrically conductive liquid 170 canvary. In the illustrated and preferred embodiment, the liquid 170comprises a hypertonic saline solution, having a sodium chlorideconcentration at or near saturation, which is about 20% weight byvolume. Hypertonic saline solution has a low resistivity of only about 5ohm.cm, compared to blood resistivity of about 150 ohm.cm and myocardialtissue resistivity of about 500 ohm.cm. Alternatively, the compositionof the electrically conductive liquid medium 170 can comprise ahypertonic potassium chloride solution. This medium, while promoting thedesired ionic transfer, requires closer monitoring of rate at whichionic transport occurs through the pores 184, to prevent potassiumoverload. When hypertonic potassium chloride solution is used, it ispreferred keep the ionic transport rate below about 1 mEq/min.

[0191] Due largely to mass concentration differentials across the pores184, ions in the medium 170 will pass into the pores 184, because ofconcentration differential-driven diffusion. Ion diffusion through thepores 184 will continue as long as a concentration gradient ismaintained across the body 164. The ions contained in the pores 184provide the means to conduct current across the body 164.

[0192] When radio frequency energy is conveyed from a generator to theelectrode 180, electric current is carried by the ions within the pores184. The RF currents provided by the ions result in no net diffusion ofions, as would occur if a DC voltage were applied, although the ions domove slightly back and forth during the RF frequency application. Thisionic movement (and current flow) in response to the applied RF fielddoes not require perfusion of liquid in the medium 170 through the pores184. The ions convey radio frequency energy through the pores 184 intotissue to a return electrode, which is typically an external patchelectrode (forming a unipolar arrangement). Alternatively, thetransmitted energy can pass through tissue to an adjacent electrode(forming a bipolar arrangement). The radio frequency energy may be usedto heat tissue (mostly ohmically) to form a lesion, or to render tissuetemporarily unresponsive.

[0193] The preferred geometry of the expandable-collapsible body isessentially spherical and symmetric, with a distal spherical contour.However, nonsymmetric or nonspherical geometries can be used. Forexample, the expandable-collapsible body may be formed with a flatteneddistal contour, which gradually curves or necks inwardly for attachmentwith the catheter tube. Elongated, cylindrical geometries can also beused.

[0194] The exemplary segmented porous zones 198 shown in FIG. 21 arewell suited for use in association with folding expandable-collapsiblebodies 164. In this arrangement, the regions that are free of porescomprise creased or folding regions 204. It should be appreciated thatthe foldable body 164 shown in FIG. 21 can also be used for otherpatterns of porous regions. The creased regions 204 can also be providedwith pores, if desired.

[0195] 2. Pore Patterns

[0196] The pattern of pores 184 that define the porous region of thebody may vary. As shown by way of example in FIGS. 15 and 16, the regionof at least the proximal ⅓ surface of the expandable-collapsible body164 is free of pores 184 and the porous region is in the form of acontinuous cap on the distal ⅓ to ½ of the body. This configuration isuseful when it is expected that ablation will occur with the distalregion of body 164 oriented in end-on contact with tissue.Alternatively, the electrically conductive porous region may besegmented into separate energy transmission zones arranged in aconcentric “bulls eye” pattern about the distal tip of the body 164.When it is expected that tissue stunning or modification will occur withthe side region of the body 164 oriented in contact with tissue, theporous region is preferably segmented into axially elongated energytransmission zones, which are circumferentially spaced about the body.

[0197] 3. Non-porous Conductive and Marking Regions

[0198]FIG. 22 shows an embodiment of an expandable-collapsible electrodestructure 206 that includes one or more nonporous, electricallyconductive regions 208 on the surface of the body 164. In theillustrated embodiment, the nonporous conductive regions 208 comprisemetal, such as gold, platinum, platinum/iridium, among others, depositedupon the expandable-collapsible body 164 by sputtering, vapordeposition, ion beam deposition, electroplating over a deposited seedlayer, or a combination of these processes. Alternatively, the nonporousconductive regions 208 can comprise thin foil affixed to the surface ofthe body. Still alternatively, the nonporous conductive regions cancomprise solid fixtures carried by the porous body 164 at or morelocations. Signal wires (not shown) within the body are electricallycoupled to the nonporous regions. The signal wires traverse the cathetertube 154 for coupling to the connectors 185 carried by the handle 160.

[0199] Various ways for attaching nonporous electrodes 208 andassociated signal wires to an expandable-collapsible electrode body 164are described in U.S. patent application Ser. No. 08/629,363, entitled“Enhanced Electrical Connections for Electrode Structures,” which isincorporated herein by reference.

[0200] The nonporous regions 208 can be used to sense electricalactivity in myocardial tissue. The sensed electrical activity isconveyed to an external controller, which processes the potentials foranalysis by the physician. The processing can create a map of electricalpotentials or depolarization events for the purpose of locatingpotential arrhythmia substrates. Once located with the nonporous regions208, the porous regions 198 can be used to convey radio frequency energyas previously described to ablate the substrates. Alternatively, or incombination with sensing electrical activities, the nonporous regions208 can be used to convey pacing signals. In this way, the nonporousregions can carry out pace mapping or entrainment mapping.

[0201] Opaque markers may be deposited on the interior surface of thebody 164 so that the physician can guide the device under fluoroscopy tothe targeted site. Any high-atomic weight material is suitable for thispurpose. For example, platinum, platinum-iridium. can be used to buildthe markers. Preferred placements of these markers are at the distal tipand center of the structure 164.

[0202] The expandable-collapsible structure 206 shown in FIG. 22 therebycombines the use of “solid” nonporous electrodes 208 with “liquid” orporous electrodes 198. The expandable-collapsible structure makespossible the mapping of myocardial tissue for therapeutic purposes usingone electrode function, and the stunning or modification of tissue fortherapeutic purposes using a different electrode function.

[0203] 4. Electrical Resistivity of the Expandable-Collapsible Body

[0204] The electrical resistivity of the body 164 has a significantinfluence on the lesion geometry and controllability. It has beendiscovered that ablation with devices that have a low-resistivity body164 (below about 500 ohm.cm) requires more RF power and results indeeper lesions. On the other hand, devices that have a high-resistivitybody 164 (at or above about 500 ohm.cm) generate more uniform heating,therefore, improve the controllability of the lesion. Because of theadditional heat generated by the increased body resistivity, less RFpower is required to reach similar tissue temperatures after the sameinterval of time. Consequently, lesions generated with high-resistivitybodies 164 usually have smaller depth. The electrical resistivity of thebody 164 can be controlled by specifying the pore size of the material,the porosity of the material, and the water adsorption characteristics(hydrophilic versus hydrophobic) of the material. A detailed discussionof these characteristics, as well as the formation of theexpandable-collapsible body, can be found in the aforementioned U.S.application Ser. No. 08/631,575, entitled “Tissue heating and AblationSystems and Methods Using Porous Electrode Structures.”

[0205] Generally speaking, pore diameters smaller than about 0.1 μmretain macromolecules, but allow ionic transfer through the pores inresponse to the applied RF field. With smaller pore diameters, pressuredriven liquid perfusion through the pores 184 is less likely toaccompany the ionic transport, unless relatively high pressureconditions develop within the body 164. Larger pore diameters (less than8 μm) prevent most blood cells from crossing the membrane, but permitpassage of ions in response to the applied RF field. With larger porediameters, pressure driven liquid perfusion, and the attendant transportof macromolecules through the pores 184, is also more likely to occur atnormal inflation pressures for the body 164.

[0206] Low or essentially no liquid perfusion through the pores 184 ispreferred because it limits salt or water overloading, caused bytransport of the hypertonic solution into the blood pool and it allowsionic transport to occur without disruption. When undisturbed byattendant liquid perfusion, ionic transport creates a continuous virtualelectrode 186 (see FIG. 20) at the body 164-tissue interface. Thevirtual electrode 186 efficiently transfers RF energy without need foran electrically conductive metal surface.

[0207] With respect to porosity, the placement of the pores 184 and thesize of the pores 184 determine the porosity of the body 164. Theporosity represents the space on the body 164 that does not containmaterial, or is empty, or is composed of pores 184. Expressed as apercentage, porosity represents the percent volume of the body 164 thatis not occupied by the body material. The magnitude of the porosityaffects the liquid flow resistance of the body 164, as discussed above.The equivalent electrical resistivity of the body 164 also depends onits porosity. Low-porosity materials have high electrical resistivity,whereas high-porosity materials have low electrical resistivity. Forexample, a material with 3% porosity, when exposed to 9% hypertonicsolution (resistivity of 5 ohm.cm), may have an electrical resistivitycomparable to that of blood or tissue (between 150 and 450 ohm.cm).

[0208] For a given a porosity value, an array of numerous smaller pores184 is typically preferred, instead of an array of fewer but largerpores, because the presence of numerous small pores 184 distributescurrent density so that the current density at each pore 184 is less.With current density lessened, the ionic flow of electrical energy totissue occurs with minimal diminution due to resistive heat loss. Anarray of numerous smaller pores 184 is also preferred because it furtherhelps to impose favorably large liquid flow resistance. It is alsopreferable that the porous body 164 possess consistent pore size andporosity throughout the desired ablation region to avoid localizedregions of higher current density and the formation of lesions that arenot therapeutic because they do not extend to the desired depth orlength.

[0209] A dynamic change in resistance across a body 164 can be broughtabout by changing the diameter of the body 164 made from a porouselastic material, such as silicone. In this arrangement, the elasticbody 164 is made porous by drilling pores of the same size in theelastic material when in a relaxed state, creating a given porosity. Asthe elastic body 164 is inflated, its porosity remains essentiallyconstant, but the wall thickness of the body 164 will decrease. Thus,with increasing diameter of the body 164, the resistance across the body164 decreases, due to decreasing wall thickness and increasing surfacearea of the body 164. The desired lesion geometry may be specifiedaccording to the geometry of the body 164. This enables use of the sameporous body 164 to form small lesions, shallow and wide lesions, or wideand deep lesions, by controlling the geometry of the body 164.

[0210] Turning to water absorption characteristics, hydrophilicmaterials are generally preferable because they possess a greatercapacity to provide ionic transfer of RF energy without significantliquid flow through the material.

[0211] D. Surgical Probes

[0212] As noted above, the present inventions are not limited tocatheter-based devices and may be incorporated into surgical probeswhich are not catheter-based. Such probes allow the physician todirectly apply the electrode or other operative element to tissue.Additional information concerning such probes, and uses thereof, may befound in U.S. patent application Ser. No. 08/949,117, entitled “Systemsand Methods for Positioning a Diagnostic or Therapeutic Element Withinthe Body,” which is incorporated herein by reference.

[0213] As illustrated for example in FIGS. 23 and 24, a surgical device(or “probe”) 210 for positioning an operative element 214 within apatient includes a relatively short shaft 216 and a substantiallytriangularly shaped spline assembly 234. The relatively short shaft maybe between approximately 4 and 18 inches in length, and is preferably 8inches in long, while the outer diameter of the shaft is preferablybetween approximately 6 and 24 French. The operative element preferablyconsists of a plurality of electrode elements 250. The spline assembly234 consists of first and second side legs 236 and 238 and a distal leg240. The distal leg 240, which is preferably non-linear from end to endand approximately 10 to 12 cm in length, includes first and secondlinear portions 242 and 244 and a bent portion 246 located mid-waybetween the ends. This spline configuration provides a spring forceagainst the selected bodily surface during use (such as the atrium wallin a cardiac procedure) and the bend in the distal leg 240 optimizes thecontact between the operative element 214 and the selected surface. Thesurgical probe 210 also includes a first handle 228 and a second handle229.

[0214] The spline assembly 234 will collapse in the manner shown in FIG.24 when a tubular member 226 (such as a sheath) is advanced thereoverand will return to the orientation shown in FIG. 23 when the tubularmember is retracted. The tubular member 226 preferably includes a raisedgripping surface 230.

[0215] During use of the exemplary surgical device shown in FIGS. 23 and24, the handle 229 is grasped by the physician and force is appliedthrough the shaft 216 and side legs 236 and 238 to the operative elementsupporting distal leg 240. The shaft 216 and side legs 236 and 238 maybe configured such that they collapse and form a semicircle with thedistal leg 240 when force is applied to the shaft. Here, the operativeelement should be appropriately masked in one of the manners describedbelow to limit contact of the operative element to the intended bodilystructure.

[0216] The exemplary embodiment illustrated in FIGS. 23 and 24 may alsobe provided without the tubular member 226. Such devices are especiallyuseful in surgical procedures associated with a thoracotomy or a mediansternotomy, where the spline assemblies can be easily collapsed andadvanced to the desired location, or advanced into the desired locationwithout being collapsed. Here, the spline assemblies can be malleable,if desired, as opposed to simply being bendable.

[0217] The spline assemblies illustrated in FIGS. 23 and 24 arepreferably made from resilient, inert wire, like nickel titanium(commercially available as Nitinol material) or 17-7 stainless steel.However, resilient injection molded inert plastic can also be used. Thewire or molded plastic is covered by suitable biocompatiblethermoplastic or elastomeric material such as PEBAX® or pellethane.Preferably, the various portions of the spline assemblies comprises athin, rectilinear strips of resilient metal or plastic material. Still,other cross-sectional and longitudinal configurations can be used. Forexample, the spline legs can decrease in cross-sectional area in adistal direction, by varying, e.g., thickness or width or diameter (ifround), to provide variable stiffness along its length. Variablestiffness can also be imparted by composition changes in materials or bydifferent material processing techniques. The distal leg 240 may beconfigured such that the leg is flat at the distal end, but becomes moresemicircular in cross-section as the leg becomes more proximal in orderto taper the stiffness profile and prevent lateral movement of thespline assembly. The curvature of the spline legs may also be varied andthe lateral ends of the distal leg may be reinforced in order to providemore lateral stability.

[0218] As shown by way of example in FIGS. 25-27, the spline assembly ofthe probe shown in FIGS. 23 and 24 may be replaced by a curved splineassembly 252. Here, the spline assembly includes a flat, inert wire 254(preferably formed from Nitinol) that acts as a spring and an outerportion 256 (preferably formed from PEBAX® or pellethane). Viewed incross-section, the flat wire 254 has a long side and a short side. Assuch, the spline assembly 252 will deflect in the manner shown in FIG.26 when “in plane” forces F are applied to the spline assembly.Conversely, the assembly will resist bending when “out of plane” forcesare applied. As such, it may be used to form an arcuate lesion during,for example, a procedure where a lesion is formed around the pulmonaryvein.

[0219] It should be noted here that the wire 254 does not have to berectangular in cross-section. Other cross-sectional shapes where thelength is greater than the width can also be used. The wire 254 can alsobe made from a malleable material such as partially or fully annealedstainless steel instead of the spring-like material discussed above. Themalleable embodiments will enable the operator to form fit the ablationelement support structure to irregular anatomical structures.

[0220] As shown in FIG. 27, exemplary spline assembly 252 may includefirst and second steering wires 251 a and 251 b that are secured to thespring-like flat wire 254 by, for example, welding or adhesive bonding.The proximal ends of the steering wires 251 a and 251 b are operablyconnected to a knob 255 on a handle 248 by way of a cam (not shown). Thehandle 248 also includes provisions for the steering wires 251 a and 251b. Rotation of the knob 255 will cause the spline assembly to move sideto side. Thus, in addition to simply moving the handle, the physicianwill be able to move the operative element 214 within the patient byrotating the knob 255. Such movement is useful when the physician isattempting to precisely locate the operative element within the patientand/or control the contact force between the operative element and thetissue surface. This is especially true when the handle and or shaft 216cannot be moved, due to anatomical or surgical constraints.

[0221] In the exemplary embodiment shown in FIG. 27, the steering wires251 a and 251 b are both secured at about the midpoint of the flat wireloop. Other configurations are possible depending on the configurationof the loop that is desired after the knob 255 is rotated. For example,one wire could be secured closer to the top of the loop than the other.The shape of the cam may also be varied. More detailed discussions ofthe use of steering wires, albeit in conventional catheter settings, canbe found in commonly assigned U.S. Pat. Nos. 5,195,968, 5,257,451, and5,582,609, which are incorporated herein by reference.

[0222] The shaft 216 is preferably relatively stiff. As used herein thephrase “relatively stiff” means that the shaft (or other structuralelement) is either rigid, malleable, or somewhat flexible. A rigid shaftcannot be bent. A malleable shaft is a shaft that can be readily bent bythe physician to a desired shape, without springing back when released,so that it will remain in that shape during the surgical procedure.Thus, the stiffness of a malleable shaft must be low enough to allow theshaft to be bent, but high enough to resist bending when the forcesassociated with a surgical procedure are applied to the shaft. Asomewhat flexible shaft will bend and spring back when released.However, the force required to bend the shaft must be substantial. Rigidand somewhat flexible shafts are preferably formed from stainless steel,while malleable shafts are formed from annealed stainless steel.

[0223] One method of quantifying the flexibility of a shaft, be itshafts in accordance with the present invention or the shafts ofconventional catheters, is to look at the deflection of the shaft whenone end is fixed in cantilever fashion and a force normal to thelongitudinal axis of the shaft is applied somewhere between the ends.Such deflection (σ) is expressed as follows:

σ=WX²(3L−X)/6EI

[0224] where:

[0225] W is the force applied normal to the longitudinal axis of theshaft,

[0226] L is the length of the shaft,

[0227] X is the distance between the fixed end of the shaft and theapplied force,

[0228] E is the modulous of elasticity, and

[0229] I is the moment of inertia of the shaft.

[0230] When the force is applied to the free end of the shaft,deflection can be expressed as follows:

σ=WL³/3EI

[0231] Assuming that W and L are equal when comparing different shafts,the respective E and I values will determine how much the shafts willbend. In other words, the stiffness of a shaft is a function of theproduct of E and I. This product is referred to herein as the “bendingmodulus.” E is a property of the material that forms the shaft, while Iis a function of shaft geometry, wall thickness, etc. Therefore, a shaftformed from relatively soft material can have the same bending modulusas a shaft formed from relatively hard material, if the moment ofinertia of the softer shaft is sufficiently greater than that of theharder shaft.

[0232] For example, a relatively stiff 2 inch shaft (either malleable orsomewhat flexible) would have a bending modulus of at leastapproximately 1 lb.-in.² Preferably, a relatively stiff 2 inch shaftwill have a bending modulus of between approximately 3 lb.-in.² andapproximately 50 lb.-in.². By comparison, 2 inch piece of a conventionalcatheter shaft, which must be flexible enough to travel through veins,typically has bending modulus between approximately 0.1 lb.-in.² andapproximately 0.3 lb.-in.². It should be noted that the bending modulusranges discussed here are primarily associated with initial deflection.In other words, the bending modulus ranges are based on the amount offorce, applied at and normal to the free of the longitudinal axis of theshaft, that is needed to produce 1 inch of deflection from an at rest(or no deflection) position.

[0233] As noted above, the deflection of a shaft depends on thecomposition of the shaft as well as its moment of inertia. The shaftcould be made of elastic material, plastic material, elasto-plasticmaterial or a combination thereof. By designing the shaft 216 to berelatively stiff (and preferably malleable), the surgical tool is betteradapted to the constraints encountered during the surgical procedure.The force required to bend a relatively stiff 2 inch long shaft shouldbe in the range of approximately 1.5 lbs. to approximately 12 lbs. Bycomparison, the force required to bend a 2 inch piece of conventionalcatheter shaft should be between approximately 0.2 lb. to 0.25 lb.Again, such force values concern the amount of force, applied at andnormal to the free of the longitudinal axis of the shaft, that is neededto produce 1 inch of deflection from an at rest (or no deflection)position.

[0234] Ductile materials are preferable in many applications becausesuch materials can deform plastically before failure due to fracturing.Materials are classified as either ductile or brittle, based upon thepercentage of elongation when the fracture occurs. A material with morethan 5 percent elongation prior to fracture is generally consideredductile, while a material with less than 5 percent elongation prior tofracture is generally considered brittle. Material ductility can bebased on a comparison of the cross sectional area at fracture relativeto the original cross area. This characteristic is not dependent on theelastic properties of the material.

[0235] Alternatively, the shaft could be a mechanical component similarto shielded (metal spiral wind jacket) conduit or flexible Loc-Line®,which is a linear set of interlocking ball and socket linkages that canhave a center lumen. These would be hinge-like segmented sectionslinearly assembled to make the shaft.

[0236] The exemplary tubular member 226 illustrated in FIGS. 23 and 24is preferably in the form of a relatively thin cylindrical sheath (e.g.,with a wall thickness of about 0.005 inch) and has an outer diameterwhich is preferably less than 0.180 inch. The sheath material ispreferably also lubricious, to reduce friction during movement of thesheath relative to the shaft 216 and spline assembly 234. For example,materials made from polytetrafluoroethylene (PTFE) can be used for thesheath. The distal end of the sheath should be relatively flexible toprevent injury. If necessary, additional stiffness can be imparted tothe remaining portion of the sheath by lining the sheath with a braidedmaterial coated with PEBAX® material (comprising polyethel block amiderelated to nylon). Other compositions made from PTFE braided with astiff outer layer and other lubricious materials can be used.

[0237] Alternatively, the tubular member 226 may be relatively stiff andformed from the materials described above with respect to the shaft 216.

[0238] As shown by way of example in FIG. 28, a surgical probe 260 inaccordance with another embodiment of a present invention includes arelatively stiff shaft 262, a handle 264 and a distal section 266. Theshaft 262 consists of a hypotube 268, which is either rigid orrelatively stiff, and an outer polymer tubing 270 over the hypotube. Arelatively stiff tube, either malleable or somewhat flexible, willpreferably have a bending modulus of between approximately 3 lb.-in.²and approximately 50 lb.-in.². The handle 264 is similar to the handle228 discussed above in that it includes a PC board 272 for connectingthe operative elements on the distal portion of the probe to a powersource. The handle 264 preferably consists of two molded handle halvesand is also provided with strain relief element 274. An operativeelement 214 (here, in the form of a plurality of electrode elements 54)is provided on the distal section 266. This embodiment is particularlyuseful because it can be easily inserted into the patient through anintroducing port such as a trocar.

[0239] In those instances where a malleable shaft 262 is desired, thehypotube 268 may be the heat treated malleable hypotube 268 shown inFIGS. 28 and 32. By selectively heat treating certain portions of thehypotube, one section of the hypotube (preferably the distal section)can be made more malleable than the other. This will alleviate anydiscontinuity between the distal section 266 and the shaft 262 when thedistal section is malleable.

[0240] The distal section 266 can be either somewhat flexible, in thatit will conform to a surface against which it is pressed and then springback to its original shape when removed from the surface or, as notedabove, malleable. A bending modulus of between 3 lb.-in.² and 50 lb.-n.²is preferred. As shown by way of example in FIG. 30, a somewhat flexibledistal section 266 may include a spring member 280, which is preferablyeither a solid flat wire spring (as shown) or a three leaf flat wireNitinol spring, that is connected to the distal end of the hypotube 268.Other spring members, formed from materials such as 17-7 or carpenter'ssteel, may also be used. A series of lead wires 282 and 284 connect theelectrode elements 250 and temperature sensor elements (discussedbelow), respectively, to the PC board 272. The spring member 280 andleads wires 282 and 284 are enclosed in a flexible body 286, preferablyformed from PEBAX® material, polyurethane, or other suitable materials.The spring member 280 may also be pre-stressed so that the distal tip ispre-bent in the manner shown in FIG. 28. Also, an insulating sleeve 281may be placed between the spring member 280 and the lead wires 282 and284.

[0241] In those instances where a malleable distal section 266 isdesired, the spring member 280 may be replaced by a mandrel 287 made ofsuitably malleable material such as annealed stainless steel orberyllium copper, as illustrated for example in FIG. 31. The mandrelwill ideally be fixed to the distal tip of the device (by, for example,soldering, spot welding or adhesives) and run through the shaft into thehandle where it will also be fixed to insure good torque transmissionand stability of the distal tip. Alternatively, the malleable mandrelmay be fixed directly within the distal end of the shaft's hypotube 268and secured by, for example, soldering, spot welding or adhesives.

[0242] The distal section 266 may also be formed by a hypotube that issimply a continuation of the shaft hypotube 268. However, the distal endhypotube can be a separate element connected to the shaft hypotube 268,if it is desired that the distal end hypotube have different stiffness(or bending) properties than the shaft hypotube.

[0243] The shaft 262 may be from 4 inches to 18 inches in length and ispreferably 6 to 8 inches. The distal section 266 may be from 1 inch to10 inches in length and is preferably 2 to 3 inches. The length of theelectrode elements may range from approximately 4 mm to approximately 20mm. To facilitate the formation of long continuous lesions or areas ortemporarily unresponsive tissue, the distal section 266 preferablyincludes six electrode elements 250 that are approximately 12 mm inlength and approximately 2 to 3 mm apart. This aspect of the inventionsis discussed in Section II-A above with reference to FIGS. 6-8. Thenumber and length of the electrode elements 250 can, of course, bevaried to suit particular applications.

[0244] In accordance with some embodiments of the invention, and asshown by way of example in FIG. 29, the distal section 266 may beprovided with a distal (or tip) electrode. The distal electrode 276 maybe a solid electrode with a through hole for one or more temperaturesensors. Distal electrodes have a variety of applications. For example,a distal electrode may be dragged along an anatomical surface to createa long lesion. The distal electrode may also be used to touch up lesionsor areas of unresponsive tissue (straight or curvilinear) created byelectrode elements 250 if, for example, the distal section 266 does notexactly conform to the anatomical surface, and to continue lesions andareas of temporarily unresponsive tissue formed by the electrodeelements. The distal electrode may also be used to create lesions andareas of temporarily unresponsive tissue in anatomical ridges that areshaped such that the integrity of the surgical device would becompromised if the distal section 266 were bent to conform to the ridge.

[0245] In the exemplary embodiments illustrated in FIGS. 23-35, theoperative element 214 is made up of a plurality of electrode elements250 which can serve a variety of different purposes. The operativeelements may also be devices such as lumens for chemical ablation, laserarrays, ultrasonic transducers, microwave electrodes, and D.C. hotwires. Such devices may also be incorporated into the other embodimentsdisclosed in the present specification as appropriate.

[0246] In the illustrated embodiments, the principal use of theelectrode elements 250 is to transmit electrical energy and, moreparticularly, RF energy, to modify or stun heart and other tissue.However, the electrode elements 250 can also be used to sense electricalevents in heart and other tissue. Alternatively, or in addition, theelectrode elements 250 can serve to transmit electrical pulses tomeasure the impedance of heart tissue, to pace heart tissue, or toassess tissue contact.

[0247] The electrode elements 250 are electrically coupled to individualwires (see reference numeral 288 FIG. 35 and reference numeral 282 inFIGS. 30 and 31) to conduct energy to them. The wires are passed inconventional fashion through a lumen extending through one of the splinelegs and the shaft 216 into a PC board in the handle, where they areelectrically coupled to a connector which is received in a port in thehandle. The connector can be used to plug into a source of energy, suchas RF ablation or tissue stunning, energy. A plurality of temperaturesensing elements (not shown), such as theremocouples or thermistors, mayalso be provided on the spline assemblies shown herein. Such temperaturesensing elements may be located on, under, abutting the edges of, or inbetween, the electrode elements 250. The temperature sensing elements,and the placement thereof, is discussed in detail below in Section II-F.For temperature control purposes, signals from the temperature sensorelements are transmitted to the source of energy by way of wires (seereference numeral 294 FIG. 35 and reference numeral 284 in FIGS. 30 and31) which are also connected to the PC board. The respective numbers ofwires will, of course, depend on the numbers of sensors and electrodesused in a particular application.

[0248] The electrode elements 250, as well as the other electrodesdiscussed in the present specification, can be assembled in variousways. They can, for example, comprise multiple, generally rigidelectrode elements arranged in a spaced apart, segmented relationship.The segmented electrodes can each comprise solid rings of conductivematerial, like platinum, which makes an interference fit about theannular spline member. Alternatively, the electrode segments cancomprise a conductive material, like platinum-iridium or gold, coatedupon the device using conventional coating techniques or an ion beamassisted deposition (IBAD) process. The electrodes can also be in theform of helical ribbons.

[0249] Alternatively, the electrode elements 250, as well as the otherelectrodes discussed in the present specification, can comprise spacedapart lengths of closely wound, spiral coils wrapped on the device whichform an array of generally flexible electrode elements, as discussed inSection Il-A above with reference to FIGS. 6-8. The coils are made ofelectrically conducting material, like copper alloy, platinum, orstainless steel, or compositions such as drawn-filled tubing (e.g. acopper core with a platinum jacket). The electrically conductingmaterial of the coils can be further coated with platinum-iridium orgold to improve its conduction properties and biocompatibility.

[0250] Electrode elements 250, as well as the other electrodes discussedin the present specification, can be formed with a conductive inkcompound that is pad printed onto a non-conductive tubular body. Apreferred conductive ink compound is a silver-based flexible adhesiveconductive ink (polyurethane binder), however other metal-based adhesiveconductive inks such as platinum-based, gold-based, copper-based, etc.,may also be used to form electrodes. Such inks are more flexible thanepoxy-based inks.

[0251] E. Regenerated Cellulose Coating

[0252] As illustrated for example in FIG. 33, the electrode elements250, as well as the other electrodes disclosed in the presentspecification, can include a porous material coating 296, whichtransmits ablation energy through an electrified ionic medium. Forexample, as disclosed in U.S. patent application Ser. No. 08/879,343,filed Jun. 20, 1997, entitled “Surface Coatings For Catheters, DirectContacting Diagnostic and Therapeutic Devices,” which is incorporatedherein by reference, electrode elements and temperature sensor elementsmay be coated with regenerated cellulose, hydrogel or plastic havingelectrically conductive components. With respect to regeneratedcellulose, the coating acts as a mechanical barrier between the surgicaldevice components, such as electrodes, preventing ingress of bloodcells, infectious agents, such as viruses and bacteria, and largebiological molecules such as proteins, while providing electricalcontact to the human body. The regenerated cellulose coating also actsas a biocompatible barrier between the device components and the humanbody, whereby the components can now be made from materials that aresomewhat toxic (such as silver or copper).

[0253] For applications in which the ablation electrode is in contactwith flowing blood as well as tissue, such as when the patient is not onbypass, coating electrodes with regenerated cellulose decreases theeffect of convective cooling on the electrode because regeneratedcellulose is a poor thermal conductor as compared to metal. Thus, theeffect of convective cooling by blood flowing past the regeneratedcellulose coated electrodes is diminished. This provides better controlfor a lesion-generating process because the hottest tissue temperatureis closer to the ablation electrode.

[0254] Furthermore, the regenerated cellulose coating decreases the edgeeffects attributed to delivering RF energy to an electrode having asharp transition between the conductive electrode and insulatingmaterial. The current density along the electrode and power densitywithin tissue are more uniform, which reduces the incidence and severityof char and/or coagulum formation. The more uniform current densityalong the axis of the device also results in a more uniform temperaturedistribution at the electrode, which decreases the requirement forprecise placements of the temperature sensors at the ablationelectrodes. Additionally, by coating a device with regenerated celluloseto create the outer surface, less labor-intensive methods of formingelectrodes and bonding wires to electrode surfaces can be used.

[0255] F. Temperature Control

[0256] Temperature sensing elements 298, such as thermistors orthermocouples, may be used in conjunction with any of the electrodes (orother operative elements) disclosed in the present specification.Preferably, the temperature sensing elements 298 are located at the sideedges of the electrodes where the electrodes abut the underlying,non-electrically conductive support body, such as the support body 104shown in FIGS. 6 and 8 or the polymer outer tubing 270 shown in FIG. 28.RF current densities are high at the edges because the edges are regionswhere electrical conductivity is discontinuous. The resultant rise incurrent density at the electrode edges generates localized regions ofincreased power density and, therefore, regions where highertemperatures exist. Nevertheless, the temperature sensing elements mayalso be located on, under, or in between, the electrode elements in anyof the exemplary devices disclosed herein.

[0257] In the preferred -embodiment illustrated in FIG. 8, a thin stripof electrically insulating material 295 (such as an electricallynon-conducting adhesive) is applied to the support body near the closelyspaced regions in order to minimize the presence of edge currenteffects. Additionally, the temperature sensing elements can be mountedeither on the inside surface of the electrodes or on the outside surfaceencapsulated in an epoxy or PTFE coating 297.

[0258] As illustrated for example in FIG. 15, the porous electrodestructure 162 can carry one or more temperature sensing elements 298.The sensing elements 298 are in thermal conductive contact with theexterior of the electrode structure 162 to sense conditions in tissueoutside the structure 162. Temperatures sensed by the temperaturesensing elements 298 are processed by a controller. Based upontemperature input, the controller adjusts the time and power level ofradio frequency energy transmissions by the electrode 180, to achievethe desired therapeutic objectives. Various ways for attachingtemperature sensing elements to an expandable-collapsible electrode bodyare described in U.S. patent application Ser. No. 08/629,363, entitled“Enhanced Electrical Connections for Electrode Structures,” which isincorporated herein by reference.

[0259] Additionally, a reference temperature sensing element may beprovided. For example, a reference temperature sensing element 299 maybe provided on or near the distal tip of the device shown in FIG. 28.The reference temperature sensor may, alternatively, be located in thehandle so that room temperature will be used as the reference. Anotheralternative is to use an electronic circuit to function as the referencetemperature sensor. A reference temperature sensor can also be placed onthe patient or in the operating room and the physician can simply inputthe reference temperature into the power control device. It should benoted that the accuracy of the reference temperature sensor is lessimportant in applications where the patient is on bypass because theconvective cooling effects of blood flowing past the electrodes issubstantially reduced. Also, the present surgical devices provide bettertissue contact than conventional catheter-based devices, which providesmore accurate temperature monitoring.

[0260] Suitable power controllers which control power to an electrodebased on a sensed temperature are disclosed in U.S. Pat. Nos. 5,456,682and 5,582,609, and the aforementioned U.S. patent application Ser. No.08/949,117, each of which are incorporated herein by reference.

[0261] III. Modes of Operation

[0262] The operating modes are discussed in the context of cardiactreatment. Nevertheless, and as noted above, the present inventions maybe used to treat other types of tissue.

[0263] A. Stunning Mode

[0264] Referring to FIGS. 1 and 5, in the stunning (or first) mode, thegenerator 46 transmits via the switching element 80 one or more highvoltage pulses through one or more of the electrode(s) discussed aboveinto a local tissue region contacting or otherwise near theelectrode(s). Operation of the switching element 80 is discussed inSection III-C. The electrode configuration may be in the form of asingle electrode, a series of spaced electrodes, or anexpandable-collapsible electrode structure. Thus, references to“electrode(s)” in this section are references to all of the electrodeconfigurations disclosed in the present specification. Each pulse has aprescribed waveform shape and duration that temporarily “stuns” tissuein the local region without field stimulating tissue in regions fartheraway from the electrode(s). The temporary stunning creates a likewisetemporary electrical conduction block in the local region, rendering thetissue region electrically unresponsive to spontaneous or induceddepolarization events. By observing the effect of the local conductionblock upon ongoing cardiac events, the physician obtains diagnosticinformation helpful in locating and confirming potential tissuemodification sites.

[0265] By purposeful operation of the electrode(s) in the stunning modein regions where the process controller 32 has assigned a potentialablation site, the system 10 is able to confirm and cross-check thelocation output of the process controller 32 to verify the location of apotentially efficacious modification site before actually modifyingtissue.

[0266] By way of example, the site appropriate for ablation to cure VTtypically constitutes a slow conduction zone, designated SCZ in FIG. 4.Depolarization wave fronts (designated DWF in FIG. 4) entering the slowconduction zone SCZ (at site A in FIG. 4) break into errant, circularpropagation patterns (designated B and C in FIG. 4), called “circusmotion.” The circus motions disrupt the normal depolarization patterns,thereby disrupting the normal contraction of heart tissue to cause thecardiac event.

[0267] The event-specific templates T(i) generated by the processcontroller 32 record these disrupted depolarization patterns. When apacing signal is applied to a slow conduction zone, the pacing signalgets caught in the same circus motion (i.e., paths B and C in FIG. 4)that triggers the targeted cardiac event. A large proportion of theassociated pacing morphologies P(i) at the sensing electrodes E(i) willtherefore match the morphologies recorded during the targeted cardiacevent.

[0268] However, when a pacing signal is applied outside a slowconduction zone, the pacing signal does not get caught in the samecircus motion. It propagates free of circus motion to induce asignificantly different propagation pattern than the one recorded duringthe targeted cardiac event. A large proportion of the pacingmorphologies P(i) at the sensing electrodes E(i) therefore do not matchthose recorded during the targeted cardiac event. The difference inpropagation patterns between pacing inside and outside a slow conductionzone is particularly pronounced during entrainment pacing. For thisreason, entrainment pacing is preferred.

[0269] Ablating or otherwise modifying tissue in or close to the slowconduction zone (designated SCZ in FIG. 4) prevents subsequentdepolarization. The destroyed tissue is thereby “closed” as a possiblepath of propagation. Depolarization events bypass the ablated region andno longer become caught in circus motion. In this way, ablation canrestore normal heart function in the treatment of VT. In treating VT,the physician therefore places the electrode(s) in a located tissueregion where the process controller 32 identifies potential efficaciousablation site. The process controller 32 can include a homing module 70to aid the physician in guiding the electrode(s) in the located region.Systems and methods for operating the homing module 70 are disclosed inU.S. Pat. No. 5,722,402, and entitled “Systems and Methods for GuidingMovable Electrode Elements Within Multiple Electrode Structures”, whichis incorporated herein by reference.

[0270] With the electrode(s) in position, and before transmittingablation energy, the physician conditions the generator 46 through theswitching element 80 for operation in the stunning mode. The physicianalso conditions the process controller 32 to induce the cardiac event tobe treated, which in this example is VT, unless the cardiac event isotherwise spontaneously occurring. As the cardiac event occurs, theelectrode(s) transmits one or more stunning pulses into the tissueregion nearest to it. The stunning pulses are timed to the localelectrogram to be transmitted when local depolarization occurs.

[0271] When the selected pulse stuns tissue laying in themodification-targeted zone, the temporarily rendering of this zoneelectrically unresponsive will temporarily interrupt the cardiacepisode, just as ablation in the zone will permanently stop the cardiacepisode. In this respect, stunning serves as a temporary preview of theintended permanent modification.

[0272] Should the stunning interrupt the cardiac episode, the physicianwaits for the temporary conduction block to resolve. Typically, thiswill take about 30 seconds. When a cardiac episode is interrupted, somearrhythmias will not spontaneously recur immediately after the temporaryconduction block has resolved. Here, the episode must be re-induced byconventional programmed stimulation, burst pacing, or other inductionmethods. After the physician confirms the similarity of the episode tothe previous targeted event, the physician may repeat the transmissionof one or more stunning pulses to confirm the interruption of theepisode. Such a procedure confirms that the substrate which is causingthe event, and which is targeted for ablation, is near the electrode(s).

[0273] If the episode continues uninterrupted despite the transmissionof one or more stunning pulses, the physician knows that the stunnedtissue does not include the targeted slow conduction zone. In thiscircumstance, the physician repositions the electrode(s) to a differentlocation geometrically near to the last stunned site. The physiciantransmits one or more stunning pulses into tissue at the new site andobserves the effect upon the spontaneous or induced episode.

[0274] The physician repeats these steps, operating the electrode(s) inthe stunning mode in the vicinity of all tissue regions the processcontroller 34 assigns a potential ablation site, until a site wherestunning consistently interrupts the arrhythmia or other condition islocated.

[0275] When the stunning pulse or pulses repeatedly interrupt thespontaneous or induced episode at a given site, the physician targetsthe site for ablation. The physician can titrate the volume of tissuecomprising the slow conduction zone by varying the amplitude of thestunning pulse and observing the effect. Having targeted themodification site and titrated its volume, the physician, withoutaltering the position of the electrode(s), conditions the generator 46through the switching element 80 for operation in the modification mode.

[0276] As noted above, some cases of VT can be cured with lesions thatare somewhat shallower than those typically used to cure VT. Inaccordance with a present invention, the electrode(s) can be used tostun tissue to a relatively shallow depth. A relatively shallow lesionwill be created if the relatively shallow area of unresponsive tissueprevents VT. Otherwise, progressively deeper areas of tissue can bestunned and tested until the VT is eliminated. This way, the depth ofthe permanently modified tissue will be no greater than necessary.

[0277] Another method of identifying appropriate ablation sites in theVT treatment context involves the identification of fractionatedelectrograms. Fractionated electrograms, in normal sinus rhythm orduring VT, are usually seen at sites where ablation or other suitabletissue modification will cure VT. However, they are also seen at siteswhere ablation does not cure VT. In accordance with a present invention,once fractionated electrogram sites are identified, VT can be inducedand stunning voltages applied. Sites that interrupt VT are goodcandidates for ablation. Nevertheless, testing at a given site should berepeated because spontaneous interruption of VT commonly occurs.

[0278] The three-dimensional electrode arrays shown by way of example inFIGS. 2 and 9-13B are particularly useful here. Stunning voltages can besequentially applied to all sites at which fractionated electrograms areobserved. In most patients, fewer than 20 electrode pairs exhibit thismorphologic feature. Even if only one stunning pulse were delivered persecond to these sites, which is a relatively slow pace, a likelyablation site could be identified in only 20 seconds. A sequentialstunning exercise could be performed in less that 20 seconds. If apatient is in VT when the sequence is initiated, one stunning pulsecould be delivered for each heart beat. As VT heart rates are usuallyfaster than 180 beats/minute (or 3/sec), all potential ablation sitescould be stunned in less than 10 seconds. A record showing whichstunning pulse was effective in terminating VT could also be recorded.

[0279] Turning to the treatment of AFIB, the physician can createcontinuous long, thin areas of electrically unresponsive tissue and thenperform testing to insure that the permanent modification of thetemporarily unresponsive tissue would create the desired therapeuticeffect. For example, the physician can perform the portions of a mazeprocedure that are common to most patients and then observe the surfaceECG to determine whether or not AFIB is continuing. In surgical cases,the atrial rhythm can be directly observed, and reading the ECG is notrequired. If the patient has spontaneously converted to normal sinusrhythm or atrial flutter, then the physician can attempt to reinduceatrial fibrillation by burst pacing the atrium at several differentsites. When AFIB persists or is inducible, the physician can use theelectrode(s) to temporarily form one or more areas of electricallyunresponsive tissue. The testing is then repeated and, if AFIB is nolonger present, those areas of tissue can be made permanentlyelectrically unresponsive. If AFIB continues to persist, the physiciancan continue to render areas both permanently and temporarilyunresponsive until a suitable combination of lesions is completed.

[0280] In accordance with another aspect of this invention,three-dimensional structures (or baskets) such as those shown in U.S.Pat. No. 5,545,193 can be used to create an entire maze pattern oftemporarily electrically unresponsive tissue. If subsequent testing doesnot show that AFIB has been eliminated, baskets that produce slightlydifferent maze patterns can be employed until the proper pattern isidentified. The tissue can then be permanently modified with the samethree-dimensional structure that was used to form the partial orcomplete maze pattern of stunned tissue, provided that the electrodes onthe structure are configured for permanent tissue modification. If it isnot configured for ablation or other modification, the three dimensionalstructure can be removed or left in the body to provide a map of theeventual modification sites.

[0281] In accordance with another aspect of this invention,three-dimensional structures (or baskets), such as those shown in U.S.Pat. No. 5,647,870, can be used to create an entire maze pattern oftemporarily electrically unresponsive tissue. If subsequent testing doesnot show that AFIB has been eliminated, then a different set ofelectrodes can be used to create a different maze pattern of temporarilyelectrically unresponsive tissue and the testing can be repeated. Thisprocess can be continued until a proper maze pattern has beenidentified. Then, with the diagnostic basket still in place, therapeuticcatheter(s) or probes can be manipulated to create the maze patternidentified by the diagnostic stunning procedure described above.Guidance of therapeutic catheters to the desired locations near thebasket stunning sites can be facilitated using the locating and guidingtechniques described in U.S. Pat. No. 5,722,416. Alternatively, the samethree-dimensional structures may be used to create therapeutic lesionsby employing the high-voltage tissue modification techniques disclosedin Section III-C below.

[0282] The effect of a stunning pulse lasts much longer than the amountof time required to deliver the stunning pulse. Typically, the effectlasts more than 100 times longer. Thus, a series of pulses delivered inrapid sequence can be used to create a complex pattern of temporarilyunresponsive tissue. Electrode support structures and energy deliverysystems such as those shown in FIGS. 10-13B, 38 and 39 may be used todeliver a series of stunning pulses. For example, a sequence of 10 msecstunning pulses, with 10 msecs between each pulse, could be applied with50 different electrodes in one second to create an entire set ofintersecting linear regions of temporarily unresponsive tissue. In otherwords, a temporary maze pattern that would block transmission of aexcitation waveform could be created in one second, or less if thepattern requires fewer electrodes. If the temporary maze patternsuccessfully terminates AF, then the physician will know that a curativelesion set for the patient may have been identified. Because stunning isreversible, the successful pattern can be repeated to confirm that theproposed pattern will be therapeutic for the patient.

[0283] Arrhythmias can appear when there are gaps in the long lesionsformed to treat AFIB or when there is a gap between a lesion and theanatomical barrier that the lesion should extend to. For example, duringthe treatment of AFIB, lesions are created between the pulmonary veinsand between the pulmonary veins and the mitral valve annulus. Theinventors herein have determined that gaps in lesions at the mitralvalve annulus are common because the myocardium is thicker at this siteand because anatomical structures at the mitral valve annulus make itdifficult to obtain tissue contact that will result in a continuouslesion, even in patients with easily induced AF or those in chronic AF.

[0284] These gaps are very difficult to locate and treat usingconventional roving catheter or probe technology partly because theprocess of defining the location and extent of the rotor circuit is timeconsuming and laborious. With such technologies, location of theappropriate ablation site commonly requires 2-4 hours of procedure time.Use of a three-dimensional structure (or basket), such as those shown inU.S. Pat. No. 5,547,870, can dramatically reduce the time required toidentify a potential ablation site. However, even with this technology,the mapping information does not provide a definitive site for curingthe arrhythmia using tissue modification methods.

[0285] The electrical stunning techniques described herein provide aneffective method of determining whether ablation at a potential sitewill cure an arrhythmia. If the flutter is eliminated, the suspected gapareas can be rendered permanently electrically unresponsive by ablationor other suitable means.

[0286] In certain situations, an alternative strategy whereby tissue isstunned at known anatomical positions is more efficient. The approximatepositions of the areas of electrically unresponsive tissue to be createdby the therapeutic catheters can be identified with fluoroscopic orultrasonic imaging. Stunning pulses are then applied to sites that areknown to be probable gap locations based on prior experience. Forexample, unwanted gaps between a line of block and an anatomical barrierare somewhat common, especially at the mitral valve, tricuspid annulusand pulmonary veins. If a stunning pulse applied to the suspected gaparea eliminates the flutter, then the area can be permanently renderedelectrically unresponsive by ablation or other suitable means.

[0287] In an alternative embodiment, the physician stuns the selectedlocal region and then operates the process controller 34 to induce thedesired cardiac event. In this embodiment, the physician observeswhether stunning the selected local region suppresses the undesiredcardiac event. When stunning a given selected region consistentlysuppresses the undesired cardiac event, which in the absence of stunningoccurs, the physician targets the given region for ablation or othermodification.

[0288] It should be appreciated that the use of high voltage stunningcan be carried out in association with conventional electrocardiogramanalysis, without the use of a multiple electrode mapping probedescribed above. The use of a multiple electrode mapping probe ispreferred, as it provides a more accurate indication where stunningshould be applied than conventional techniques.

[0289] It should also be appreciated that the stunning pulses canalternatively comprise DC or AC energy transmitted by the electrode 36from a source separate from the generator 46.

[0290] B. Power Considerations Associated With Stunning

[0291] The waveform pattern, duration, and amplitude of the stunningpulses effective to stun an efficacious volume of myocardium can beempirically determined by in vivo or in vitro tests and/or computermodeling.

[0292] The character of the stunning pulse is expressed in terms of itswaveform shape, its duration, and its amplitude. The duration andamplitude are selected so as to create a temporary electrical conductionblock without damage to the tissue. For the purpose of thisSpecification, the term “temporary” refers to a time period less thanabout five minutes.

[0293] The duration of the pulse can vary from microseconds up toseveral seconds, depending upon the waveform (DC or AC) of the pulse,amplitude of the pulse, and the electrode configuration. There is astrength-duration relationship between pulse duration and amplitude,with short pulse patterns requiring somewhat higher voltages to stun,but not kill, tissue. Short pulse durations not exceeding about 100milliseconds are preferred. Also, because the purpose of stunning is tosimulate the effect of permanent tissue modification, it is important tonote that shallow lesions (about 5 mm) are effective in treating AFIBand some other arrhythmias, while larger and deeper lesions (up to andexceeding 1 cm) are generally required when treating VT.

[0294] The pulse amplitude, S_(AMP), selected depends upon the voltagegradient, the configuration of the electrode(s), the depth of tissuepenetration desired, and the impedance of the system, expressed asfollows:$S_{AMP} = {\left( \frac{S_{V}}{L} \right) \times \left( \frac{A}{\rho} \right) \times R}$

[0295] where:

[0296] S_(V)/L represents the local voltage gradient,

[0297] A is the cross-sectional area of the voltage gradient,

[0298] ρ is the resistivity of the tissue to be stunned, and

[0299] R is the impedance of the delivery system and electrode thattransmits the pulse.

[0300] With respect to the local voltage gradient S_(V)/L, as abenchmark, DC voltage gradients of between about 70 volts/cm and 200volts/cm that are about 10 milliseconds in duration, when delivered bydefibrillation catheters, have been shown to temporarily stun chickenembryo myocardial tissue in vitro, rendering it electricallyunresponsive. The stunning in these instances extends about 1 cm fromthe electrode when a 800 volt (DC) shock is delivered. Higher voltagegradients increase the risk of killing myocardial tissue. The durationof unresponsiveness of stunned tissue varies from 1 to 60 seconds andmore, depending upon the local voltage gradient. The effective volume ofthe local conduction block shrinks with time, as tissue exposed to lowervoltage gradients at the edges of the stunned tissue volume recoversfaster than tissue exposed to higher voltage gradients at the center ofthe stunned tissue volume. See, e.g. Jones et al., “MicrolesionFormation in Myocardial Cells by High Intensity Electric FieldStimulation,” the American Physiological Society (1987), pp. H480-H486;Jones et al., “Determination of Safety Factor for DefibrillatorWaveforms in Cultured Cell Hearts,” the American Physiological Society(1982), pp. H662-H670. Based upon the foregoing in vitro benchmarks, itis believed that a nominal voltage gradient of about 125 volts/cm can besafely selected. Voltage gradients about four times higher, i.e. 500volts/cm, are believed to kill about 50% of the cells and unintentionalapplication of such voltage gradients should be avoided.

[0301] The cross-sectional area A of the voltage gradient depends uponthe shape of the electrode(s). For example, the portions of theelectrode 36 shown in FIGS. 1 and 3 and the porous electrodes shown inFIGS. 15-20 and 22 in contact with tissue are assumed to be a sphericalsection with a radius r measured from the center of the electrode bodyto the tissue where stunning occurs. The spherical model is also usefulfor the relatively small electrodes that are sometimes used in theexemplary three-dimensional arrays shown in FIGS. 2 and 9-13B. Forexample, for r=1 cm, the quantity A (assumed to be the surface area of a½ of a sphere with radius r of 1 cm) is 2πr ² or about 6 cm². Thisassumption can be made with respect to a porous electrode when thedistal half is non-conductive.

[0302] The coil electrodes shown in FIGS. 6-8 and 23-28 form continuouscylindrically shaped transmission areas. The quantity A of the generallycylindrical coil is 2πrl (where l is the length of the coil). When thepatient is on bypass, and one half of the electrode is exposed to air,the quantity A is πrl.

[0303] Turning to the resistivity ρ of the tissue to be stunned, for anelectrode exposed to both blood and myocardial tissue, ρ is believed tobe about 200 ohm.cm, while the resistivity of myocardial tissue whenblood is not present (such as when the patient is on bypass) is about400 to 500 ohm.cm.

[0304] It is also noteworthy that larger electrodes (greater than about4 mm) require somewhat lower voltages to achieve the same stunningeffect. This is primarily because of decreased losses in near-fieldtissue because of decreased current densities at the surface of largerelectrodes.

[0305] The waveform shape and period is selected so that the pulse willnot field stimulate tissue at sites distant from the electrode(s). Astunning pulse that causes far field stimulation can cardiovert (i.e.,stop) the entire cardiac event for reasons other than a temporary,localized conduction block. Cardioversion therefore can overshadow thedesired, more discrete specificity of the stunning effect. The characterof the stunning pulse is selected to induce only a temporary conductionblock in a discrete, relatively small volume of tissue generally equalto the volume of tissue to be ablated or otherwise modified. A biphasicor uniphasic square wave (DC) transmitted for a short duration (about100 microseconds) will achieve this effect. A sinusoidal (AC) signal atfrequencies above about 10 kHz for durations of about 10 millisecondswill also achieve this effect. The DC pulse or short duration AC signalcan be transmitted either unipolar (as the illustrated embodiment shows)or in a bipolar mode.

[0306] Based upon the foregoing considerations, and assuming that bloodis present so that the effective tissue resistivity is 200 ohm.cm, foran electrode such as that shown in FIGS. 1 and 3 with a diameter ofabout 4 mm, a radio frequency pulse having an amplitude of about 100volts (at 500 kHz) and a duration of about 10 milliseconds will stuntissue to a depth of about 5 mm (which is sufficient when treating AFIBand supra-ventricular tachycardia (SVT)). With the same 4 mm electrode,a larger pulse amplitude of about 400 volts (at 500 kHz) at a durationof about 10 milliseconds will stun tissue to a deeper depth of about 1cm (which is required for treating VT). Thus, taking typical electrodeconfigurations and typical ranges of stunning depths into account, theradio frequency pulse amplitude (at 500 kHz) will range from about 100volts up to about 800 volts (at 500 kHz), with durations less than about100 milliseconds.

[0307] When the patient is on bypass with no blood present (and thetissue resistivity is about 400 to 500 ohm-cm), a radio frequency pulsehaving an amplitude of about 50 volts (at 500 kHz) and a duration ofabout 10 milliseconds will stun tissue to a depth of about 5 mm, and apulse having an amplitude of about 250 volts (at 500 kHz) and a durationof about 10 milliseconds will stun tissue to a depth of about 1 cm.

[0308] Turning to porous electrode structures, and assuming that thedistal half of the porous electrode is non-conductive so that currentflows primarily into the myocardial tissue and not into blood, whetherthe patient is on bypass or not, the tissue resistivity will be about400 to 500 ohm-cm. For a 1.2 cm balloon, stunning tissue to a depth of 5mm requires a radio frequency pulse having an amplitude of about 100volts (at 500 kHz) and a duration of about 10 milliseconds, furtherassuming a system impedance of 70 ohms. At 500 kHz, stunning tissue to adepth of 1 cm will require a pulse of about 200 volts for about 10milliseconds, stunning tissue to a depth of 1.5 cm requires a pulse ofabout 360 volts for about 10 milliseconds, and stunning tissue to a 2 cmdepth will require a pulse of about 600 volts for about 10 milliseconds.The 600 volt pulse may, however, kill 1-2 mm of tissue near theelectrode because of the very large voltage gradients at the surface ofthe porous electrode.

[0309] The power requirement calculations for the electrodes shown inFIGS. 6-8 and 23-28, which are especially useful in AFIB treatment, havebeen made with the following assumptions: the modification/stunningelectrodes are 12.5 mm long coils, the coils are exposed to blood(effective tissue resistivity of 200 ohm.cm), the current spreads incylindrical manner, the cylinder is 2 cm long (to compensate for notincluding the ends of the cylinder in the model), and the systemimpedance is 70 ohms when stunning through a single electrode. With acylindrical electrode, the voltage gradient drops as a function of 1/r.When the tissue surface is about 2 mm from the center of the coil, aradio frequency pulse having an amplitude of about 300 volts (500 kHz)and a duration of about 10 milliseconds will to stun tissue to a depthof 3 mm. Stunning to a depth of 8 mm requires an amplitude of about 600volts (500 kHz) and duration of about 10 milliseconds. Beyond 8 mm, thecylindrical model will not produce accurate approximations of thegeometry of the system, and voltage requirements rise rapidly.

[0310] The three-dimensional electrode supporting structures shown inFIGS. 2 and 9-13B are also used to stun tissue. Depending upon electrodesize and spacing, they are generally capable of creating lines oftemporarily unresponsive tissue along a spline or between splines. Whensuch structures are incorporated into a catheter-based device, the wiresto the electrodes are typically only about 42 gauge. Although sizelimits their ability to carry high currents for extended periods oftime, the wires are capable of carrying the 4 amperes of currentrequired to stun tissue for at least 10 ms.

[0311] The current requirements for the electrodes in the threedimensional arrays are about the same as that required for theconventional 4 mm electrode discussed above with reference to FIGS. 1and 3, but the driving voltage requirements are higher due to the highersystem impedance. The higher system impedance is caused by theresistance of the wires connecting the connector pins to the electrodes(about 20 ohms) and the high current density at the electrodes. Assumingthat tissue resistivity is 200 ohm-cm (the combined resistivity oftissue and blood in a non-bypass environment), a system impedance ofabout 200 ohms (we measured this in animals), and the aforementionedspherical model, a radio frequency pulse having an amplitude of about800 volts (500 kHz) and a duration of about 10 milliseconds will to stuntissue to a depth of 1 cm. A pulse with an amplitude of about 150 voltsand a duration of about 10 milliseconds will stun tissue to a depth of 5mm. It should be noted, however, that the destruction of about 1 mm³ oftissue is almost unavoidable using presently available electrodes.

[0312] Three-dimensional arrays, such as those discussed in SectionII-B, can be used in conjunction with surgical probes, preferably whenthe patient is on bypass. The stunning voltage requirements forelectrodes in the three-dimensional arrays are much lower when patientsare on bypass. No blood is present and the effective tissue resistivityis about 400-500 ohm-cm. The effective area of the voltage gradient isalso about one-half of the voltage gradient area when blood is presentbecause virtually no current flows in air. The system impedance is,however, increased to about 350 ohms. The net effect is to decrease, byabout a factor of two, the amplitude of the voltage pulse required tostun tissue to a given depth. For example, only about 400 volts would berequired to stun tissue to a depth of 1 cm. In addition, the dimensionalconstraints placed on a device that must be introduced percutaneouslyare considerably relaxed for arrays that are inserted into patients onbypass. Electrode area could easily be doubled for devices designed forintroduction into heart chambers via an atriaotomy duringcardiopulmonary bypass. Use of these larger electrodes would decreasethe amplitude of the voltage stunning pulse by an additional factor ofone and one-half, primarily because the system impedance is lower withthe larger electrodes.

[0313] It should be appreciated that the relatively high power requiredto stun tissue will also heat the tissue. As compared to the timerequired to redistribute heat in the body, stunning pulses are veryshort in duration. Thus, a stunning pulse causes an increase in thetemperature of the affected tissue based solely on the energy dissipatedin the affected tissue during the stunning pulse. Typically, a stunningpulse will directly heat 2 or more grams of tissue. The maximum powerrequired will be up to about 12,000 Watts, with a pulse duration of 1-10msec. Therefore, the stunning pulse could deliver as much as 120 Joulesto the tissue (or about 30 calories), which would immediately raise thetemperature of the affected tissue to about 50° C.

[0314] 50° C. is very close to the temperature that can kill tissue.Therefore, unless the goal is to actually destroy tissue (high voltagetissue modification is discussed in Section III-B), the pulse durationshould be limited to prevent ohmic heating to such an extent that theaffected tissue is destroyed. For example, a 1 msec long pulse is nearlyas effective at stunning tissue as is a 10 msec long pulse, but thetemperature rise with the 1 msec long pulse is {fraction (1/10)} aslarge as with a 10 msec long pulse.

[0315] C. The Modification Mode

[0316] 1. Low Voltage Modification

[0317] In the low voltage modification mode, the generator 46 transmitslower voltage radio frequency energy into a selected tissue regionthrough either the same electrode(s) that are used to stun tissue, ordifferent electrodes when the electrodes used to stun the tissue are notsuitable for tissue modification. The radio frequency energy may, forexample, have a waveform shape and duration that electrically heats andkills tissue in the selected region. When used in cardiac ablation, forexample, the generator 46 is conditioned to deliver up to 150 watts ofpower for about 10 to 120 seconds at a radio frequency of 500 kHz. Bydestroying the tissue, the radio frequency energy forms a permanentelectrical conduction block in the tissue region.

[0318]FIG. 5 shows a representative implementation for the switchingelement 80 associated with the generator 46 to change operation betweenthe stunning mode and the modification mode. In this embodiment, theswitching element input 82 (comprising supply and return lines) iscoupled to the generator 46, which delivers radio frequency energy (500kHz) at a prescribed energy input level suitable for stunning, aspreviously described. The switching element output 84 (also comprisingsupply and return lines) is coupled to the transmitting electrode(s) andto the return line electrode, designated E_(r) in FIG. 5.

[0319] The switching element 80 includes an electronic switch 92defining a first switch path 86 and a second switch path 90.

[0320] The first switch path 86 conditions the generator 46 foroperation in the stunning mode. The first switch path 86 includes afirst isolation transformer 88. The isolation transformer 88, shown inFIG. 5 as a 1:1 transformer, directs the stunning energy through theelectrode(s) without amplitude modification for stunning tissue in themanner described. In the stunning mode, the electronic switch 92transmits stunning energy through the first switch path 86 in shortcycle intervals to deliver the energy in preset stunning pulses, asalready described.

[0321] The switching element 80 also includes a second switch path 90,which conditions the generator 46 for operation in the modificationmode. The second switch path 90 includes a second step-down isolationtransformer 92, which is shown for the purpose of illustration having astep-down ratio of 3:1. The transformer 92 decreases the amplitude ofthe energy transmitted to the electrode(s) to lower levels suitable forablating or otherwise modifying tissue. In the modification mode, theelectronic switch 92 transmits energy through the second switch path 90for longer cycle intervals conducive to tissue modification.

[0322] 2. High Voltage Modification

[0323] High voltage energy pulses (such as RF pulses) can be used tokill or otherwise modify tissue in at least three ways. For example, thecreation of high voltage gradients within the tissue dielectricallybreaks down tissue structures. In addition, ohmically heating tissuewill coagulate tissue structures, while ohmically heating to very hightemperatures will vaporize tissue.

[0324] When voltage gradients at or above 500 volts/cm are induced intissue, relatively short pulse durations can be used to destroy thetissue. Although voltage amplitudes 4 to 6 times higher than those usedto stun tissue are required, the pulse duration requirements are on theorder of 0.1 msec. As a result, the total pulse energy requirements fortissue destruction is similar to that used for stunning. In onepreferred method, stunning pulses are delivered to identify tissue thatis to be destroyed or otherwise modified. After the target tissue isidentified, a tissue-destroying RF energy pulse could be delivered.

[0325] Turning to heating, a high voltage RF pulse (about 500 to 1200volts in magnitude and about 50 to 100 msec in duration) deliversrelatively high power to tissue, thereby enabling very rapid heating.Because the tissue is heated rapidly, there is essentially no convectiveheat loss during power application. These factors allow the thermalimpulse response of the system to be measured based on the applicationof a stunning pulse, and the subsequent measurement of temperature atone or more locations on the electrode. From a power control standpoint,the impulse response of the system provides very important informationas to the plant to be controlled. Short bursts of high voltage RF power,or more conventional continuous RF modification methods, may be used tothermally destroy tissue using feedback control algorithms that areoptimized with the plant characterization obtained while applying astunning pulse.

[0326] Tissue vaporization can be performed through the use of highvoltage energy pulses with a pulse duration of about 250 msec to 1 sec.There are a number of therapeutic applications for this type of tissuevaporization. For example, percutaneous myocardial revascularization(PMR), which is currently performed using laser tissue vaporization, canbe performed by using high voltage pulses to vaporize tissue. Highvoltage pulse-based tissue vaporization techniques may also be useful incertain cancer therapies and to channelize a vessel that has recentlyclotted off.

[0327] High voltage pulse-based tissue vaporization techniques canfurther be used to create a channel in soft tissue in order to gainaccess to the interior of a solid organ while maintaining hemostasis.The channel in the soft tissue would enable a diagnostic or therapeuticfunction (such as the formation of an area of modified tissue) to beperformed on the selected organ.

[0328] D. Roving Pacing Mode

[0329] In an alternative embodiment, any of the multi-purposestunning-modification probes discussed above can also be conditioned foruse by the process controller 34 as a roving pacing probe, usable intandem with the basket structure 20 to generate and verify the locationoutput during the above described sampling and matching modes.

[0330] In this arrangement, the probe 16 is deployed in the heart region12 while the multiple electrode structure 20 occupies the region 12. Inthis mode, the electrode(s) is electrically coupled to the pacing module48 (as shown in phantom lines in FIG. 1) to emit pacing signals.

[0331] In use, once the process controller 32 generates the outputlocation or locations using the electrodes 24 to pace the heart, thephysician positions the probe within the localized region near theoutput location electrode or electrodes 24. As above described, theprocess controller 32 preferably includes the homing module 70 to aidthe physician in guiding the probe 16 in the localized region within thestructure 20.

[0332] The process controller 32 conditions the pacing module 48 to emitpacing signals through the probe electrode(s) to pace the heart in thelocalized region, while the electrodes 24 record the resultingelectrograms. By pacing this localized region with the probe 16, whilecomparing the paced electrograms with the templates, the processcontroller 32 provides the capability of pacing and comparing at anylocation within the structure 20. In this way, the process controller 32generates as output a location indicator that locates a site as close toa potential ablation site as possible.

[0333] Due to the often convoluted and complex contours of the insidesurface of the heart, the basket structure 20 cannot contact the entirewall of a given heart chamber. The system 10 therefore can deploy theprobe 16 outside the structure 20 to pace the heart in those wallregions not in contact with the electrodes 24. The probe 16 can also bedeployed while the basket structure-20 occupies-the region 12 to pacethe heart in a different region or chamber. In either situation, theelectrodes 24 on the structure 20 record the resulting pacedelectrograms for comparison by the process controller 32 to thetemplates. The process controller 32 is thus able to generate an outputidentifying a location close to a potential ablation site, even when thesite lies outside the structure 20 or outside the chamber that thestructure 20 occupies.

[0334] E. Electrophysiologic Diagnosis Mode

[0335] The generator 46 can be operated in the stunning mode inassociation with the probe 16 to conduct diagnostic electrophysiologicaltesting of tissue, such as myocardial tissue, in place of or in tandemwith the mapping probe 14.

[0336] In this mode of operation, the physician conditions the generator46 to transmit through the probe electrode(s) an electrical energypulse, as previously described, which temporarily renders a zone oftissue electrically unresponsive. By sensing an electrophysiologicaleffect due to the transmitted pulse, the physician can make diagnoses.

[0337] Such sensing is useful in the myocardial area where it can beused to diagnose the cause of cardiac events. For example, bytemporarily rendering zones of myocardial tissue electricallyunresponsive using an electrical energy pulse, and sensing the resultingelectrophysiological effect, the physician can, without using themapping probe 14, locate sites of automaticity, also called pacemakersites, where arrhythmia originates. Likewise, the physician can, withoutusing the mapping probe 14, locate the path or paths that maintainarrhythmia, previously referred to as the areas of slow conduction.Furthermore, by temporarily rendering zones of myocardial tissueelectrically unresponsive using the electrical energy pulse, thephysician can selectively alter the conduction properties of the heartwithin the localized zone without otherwise changingelectrophysiological properties outside the zone. For example, thephysician can create a temporary AV block by operating the generator 46in the stunning mode, as previously described.

[0338] Based at least in part upon these diagnostic tests conducted inthe stunning mode, the physician can proceed to altering anelectrophysiological property of tissue in or near a diagnosed zone. Forexample, the physician can alter the electrophysiological property byablating tissue in or near the diagnosed zone, as above described, usingradio frequency electrical energy, or laser light energy, or an ablationfluid. The physician can also treat the diagnosed cardiac disorderwithout ablating tissue, using drugs such as quinidine, digitalis, andlidocaine.

[0339] IV. Bypass and Non-Bypass Environment Considerations

[0340] In many of the exemplary embodiments, the electrodes are exposedaround their entire peripheries. These embodiments are particularlyuseful when the heart is on bypass and there is no blood flow within theheart. Here, air acts as an insulator and produces only modestconvective cooling effects, as compared to a flowing blood pool that hasa higher convection coefficient than virtually static air. Energytransmission is, therefore, essentially limited to the RF energy that istransmitted from the portion of the electrode surface that is in contactwith the tissue to either a ground electrode, or another electrodewithin the group of electrode elements. Also, as noted above, theoverall impedance of the system will increase (as compared to asituation where blood is present). This is due to the smaller effectivesurface area between the electrode and tissue.

[0341] Both of these conditions, focused RF energy and low heatdissipation into the air, will impact the ablation because they resultin a high current density. When creating long lesions with aconventional catheter, char can be created as the tip is dragged becauseof the high current density and the difficulty in monitoring tissuetemperature and controlling power that is inherent in the draggingprocess. Many of the present inventions, however, can take advantage ofthe high current density because the electrodes are not being dragged.For example, a number of electrodes can be used to ablate simultaneouslybecause the effective (tissue contacting) surface area between all ofthe ablating electrodes is smaller and the convective cooling effectsare reduced, as compared to situations where blood is present. Thisreduces the power requirements of the system. In addition, by usingelectrodes with lower thermal mass (as compared to a conventional solidtip electrode), less heat will be retained by the electrode and bettertemperature sensing can be made at the tissue surface. This will speedup the creation of the lesions and enable better lesion creationcontrol.

[0342] In instances where the patient will not be on bypass and bloodwill be flowing past the electrodes, the portion of the electrodeelements (or other operative elements) not intended to contact tissuemay be masked through a variety of techniques. For example, a layer ofUV adhesive (or another adhesive) may be painted on preselected portionsof the electrode elements to insulate the portions of the elements notintended to contact tissue. Alternatively, a slotted sheath may bepositioned over the portion of the electrode elements not intended tocontact tissue. Deposition techniques may also be implemented toposition a conductive surface only on those portions of the splineassembly intended to contact tissue.

[0343] As shown by way of example in FIG. 34, a polymer layer 293 may bethermally fused over an electrode, such as electrode 250, to maskdesired portions of the electrodes. An exemplary process for applyingthe polymer layer is as follows. A segment of shaft tubing is cut longenough to cover the desired electrodes, and is then split in half (orother desired angle) along the axis. One half is placed over theassembled distal section so that it covers the side of the electrodesthat are to be masked. A piece of polymeric shrink tubing, preferablyRNF-100 or irradiated LDPE, is then carefully slid over the catheterdistal end, so that the mask tubing is not moved from its placement overthe electrodes and so that it stops approximately 2 cm beyond the end ofthe tubing half. The distal end is then heated in a controlled heatsource at approximately 400° F. so that the mask tubing fuses into thedistal shaft tubing along its length, and so that all of its edges arewell fused into the shaft tubing, but not fused so much that the coveredelectrodes begin to poke through. Finally, the polymeric shrink tubingis split on one end and the assembly is heated at approximately 225° F.while the polymeric shrink tubing is slowly peeled off of the fusedcatheter shaft.

[0344] Additionally, as illustrated in FIG. 35, the shape of anelectrode 250′ may be such that the metallic material in the region notintended to contact tissue is eliminated.

[0345] The masking techniques described in the preceding paragraphimprove the efficiency of, for example, an ablation procedure bydecreasing the surface area of the electrodes and, therefore, the energyrequired to heat tissue. The masking can be used to form a narrowelectrode which is sometimes desirable, even when the patient will be onbypass. The convective cooling effects of blood flowing by the electrodeare also reduced. In addition, the transmission of RF energy tounintended anatomic structures is prevented. This is especiallyimportant in epicardial applications when the ablation electrodeelements may be sandwiched between multiple anatomic structuresincluding, for example, the aorta and pulmonary artery.

[0346] It is also noteworthy that masking can be useful during bypassbecause tissue can partially wrap around the electrodes when the distalend of the device is pressed against the tissue. Such masking can alsobe used to control lesion thickness.

[0347] Although the present invention has been described in terms of thepreferred embodiment above, numerous modifications and/or additions tothe above-described preferred embodiments would be readily apparent toone skilled in the art. By way of example, but not limitation,methodologies of ablating tissue other than those described above can beused. Laser energy can be transmitted to ablate tissue and fluids likealcohol (ethanol), collagen, phenol, carbon dioxide, can also beinjected into tissue to ablate it (see, for example, U.S. Pat. No.5,385,148). It is intended that the scope of the present inventionextends to all such modifications and/or additions.

We claim:
 1. An electrophysiological method, comprising the steps of:transmitting an electrical energy pulse that temporarily renders a zoneof tissue electrically unresponsive for at least one second; and sensingan electrophysiological effect due to the transmitted pulse.
 2. A methodas claimed in claim 1 , further comprising the step of: altering anelectrophysiological property of the tissue in or near the zone based,at least in part, upon the sensed electrophysiological effect.
 3. Amethod as claimed in claim 2 , wherein the step of altering anelectrophysiological property comprises ablating the tissue in or nearthe zone.
 4. A method as claimed in claim 3 , wherein the step ofablating tissue comprises applying electrical energy to the tissue in ornear the zone.
 5. A method as claimed in claim 1 , wherein thetransmitted electrical energy pulse comprises a radio frequency energywaveform.
 6. A method as claimed in claim 1 , further comprising thestep of: modifying the tissue in or near the zone based, at least inpart, upon the sensed electrophysiological effect.
 7. A method asclaimed in claim 1 , wherein the zone comprises an elongate continuouszone.
 8. A method as claimed in claim 1 , wherein the transmittedelectrical energy pulse comprises a plurality of electrical energypulses transmitted at spaced locations.
 9. An electrophysiologicalmethod, comprising the steps of; sensing at least one electrical eventin a region of tissue; transmitting into an area of the region anelectrical energy pulse that temporarily renders tissue in the areaelectrically unresponsive for at least one second; and sensing a changein the electrical event while the tissue in the area is electricallyunresponsive.
 10. A method as claimed in claim 9 , further comprisingthe step of; altering an electrophysiological property of the tissue inor near the area based, at least in part, upon the sensedelectrophysiological effect.
 11. A method as claimed in claim 10 ,wherein the step of altering an electrophysiological property comprisesablating the tissue in or near the area.
 12. A method as claimed inclaim 11 , wherein the step of ablating tissue comprises applyingelectrical energy to the tissue in or near the area.
 13. A method asclaimed in claim 9 , wherein the transmitted electrical energy pulsecomprises a radio frequency energy waveform.
 14. A method as claimed inclaim 9 , further comprising the step of: modifying the tissue in ornear the zone based, at least in part, upon the sensedelectrophysiological effect.
 15. A method as claimed in claim 9 ,wherein the area comprises an elongate continuous area.
 16. A method asclaimed in claim 1 , wherein the transmitted electrical energy pulsecomprises a plurality of electrical energy pulses transmitted at spacedlocations.
 17. An electrophysiological system, comprising an energytransmission device; and an energy source, coupled to the energytransmission device, adapted to transmit an energy pulse through theenergy transmission device that temporarily renders a zone of tissueelectrically unresponsive for at least one second.
 18. A system asclaimed in claim 17 , further comprising: a sensing device adapted tosense an electrophysiological effect due to the transmitted pulse.
 19. Asystem as claimed in claim 17 , wherein the energy source is adapted totransmit energy through the energy transmission device that alters anelectrophysiological property of the tissue in or near the zone.
 20. Asystem as claimed in claim 17 , wherein the energy pulse comprises anelectrical energy pulse.
 21. A system as claimed in claim 17 , whereinthe energy pulse comprises a frequency energy waveform.
 22. A system asclaimed in claim 17 , wherein the energy transmission device comprisesan electrode.
 23. A system as claimed in claim 17 , wherein the energytransmission device comprises a plurality of spaced electrodes.
 24. Asystem as claimed in claim 23 , wherein the plurality of electrodesdefine spacing therebetween such that the zone of electricallyunresponsive tissue is a continuous zone that spans the area between theelectrodes.
 25. A system as claimed in claim 24 , wherein the energypulse comprises a plurality of energy pulse transmitted sequentiallythrough respective electrodes in the plurality of spaced electrodes. 27.A system as claimed in claim 17 , wherein the energy transmission devicecomprises a porous electrode.
 28. A system as claimed in claim 17 ,further comprising: a relatively short shaft defining a distal end and aproximal end, the distal end supporting the energy transmission device;a handle associated with the proximal end of the relatively short shaft.29. A system as claimed in claim 26 , wherein the relatively short shaftis malleable.